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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="operators">

  <title>SQL Operators</title>

  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="Data Analysts"/>
      <data name="Category" value="Developers"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      <indexterm audience="hidden">operators</indexterm>
      SQL operators are a class of comparison functions that are widely used within the <codeph>WHERE</codeph> clauses of
      <codeph>SELECT</codeph> statements.
    </p>

    <p outputclass="toc inpage"/>

  </conbody>

  <concept rev="1.4.0" id="arithmetic_operators">

    <title>Arithmetic Operators</title>

    <conbody>

      <p>
        <indexterm audience="hidden">arithmetic operators</indexterm>
        The arithmetic operators use expressions with a left-hand argument, the operator, and then (in most cases) a right-hand argument.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>left_hand_arg</varname> <varname>binary_operator</varname> <varname>right_hand_arg</varname>
<varname>unary_operator</varname> <varname>single_arg</varname>
</codeblock>

      <ul>
        <li>
          <codeph>+</codeph> and <codeph>-</codeph>: Can be used either as unary or binary operators.
          <ul>
            <li>
              <p>
                With unary notation, such as <codeph>+5</codeph>, <codeph>-2.5</codeph>, or <codeph>-<varname>col_name</varname></codeph>,
                they multiply their single numeric argument by <codeph>+1</codeph> or <codeph>-1</codeph>. Therefore, unary
                <codeph>+</codeph> returns its argument unchanged, while unary <codeph>-</codeph> flips the sign of its argument. Although
                you can double up these operators in expressions such as <codeph>++5</codeph> (always positive) or <codeph>-+2</codeph> or
                <codeph>+-2</codeph> (both always negative), you cannot double the unary minus operator because <codeph>--</codeph> is
                interpreted as the start of a comment. (You can use a double unary minus operator if you separate the <codeph>-</codeph>
                characters, for example with a space or parentheses.)
              </p>
            </li>

            <li>
              <p>
                With binary notation, such as <codeph>2+2</codeph>, <codeph>5-2.5</codeph>, or <codeph><varname>col1</varname> +
                <varname>col2</varname></codeph>, they add or subtract respectively the right-hand argument to (or from) the left-hand
                argument. Both arguments must be of numeric types.
              </p>
            </li>
          </ul>
        </li>

        <li>
          <p>
            <codeph>*</codeph> and <codeph>/</codeph>: Multiplication and division respectively. Both arguments must be of numeric types.
          </p>

          <p>
            When multiplying, the shorter argument is promoted if necessary (such as <codeph>SMALLINT</codeph> to <codeph>INT</codeph> or
            <codeph>BIGINT</codeph>, or <codeph>FLOAT</codeph> to <codeph>DOUBLE</codeph>), and then the result is promoted again to the
            next larger type. Thus, multiplying a <codeph>TINYINT</codeph> and an <codeph>INT</codeph> produces a <codeph>BIGINT</codeph>
            result. Multiplying a <codeph>FLOAT</codeph> and a <codeph>FLOAT</codeph> produces a <codeph>DOUBLE</codeph> result. Multiplying
            a <codeph>FLOAT</codeph> and a <codeph>DOUBLE</codeph> or a <codeph>DOUBLE</codeph> and a <codeph>DOUBLE</codeph> produces a
            <codeph>DECIMAL(38,17)</codeph>, because <codeph>DECIMAL</codeph> values can represent much larger and more precise values than
            <codeph>DOUBLE</codeph>.
          </p>

          <p>
            When dividing, Impala always treats the arguments and result as <codeph>DOUBLE</codeph> values to avoid losing precision. If you
            need to insert the results of a division operation into a <codeph>FLOAT</codeph> column, use the <codeph>CAST()</codeph>
            function to convert the result to the correct type.
          </p>
        </li>

        <li id="div" rev="IMPALA-278">
          <p>
            <codeph>DIV</codeph>: Integer division. Arguments are not promoted to a floating-point type, and any fractional result
            is discarded. For example, <codeph>13 DIV 7</codeph> returns 1, <codeph>14 DIV 7</codeph> returns 2, and
            <codeph>15 DIV 7</codeph> returns 2. This operator is the same as the <codeph>QUOTIENT()</codeph> function.
          </p>
        </li>

        <li>
          <p>
            <codeph>%</codeph>: Modulo operator. Returns the remainder of the left-hand argument divided by the right-hand argument. Both
            arguments must be of one of the integer types.
          </p>
        </li>

        <li>
          <p>
            <codeph>&amp;</codeph>, <codeph>|</codeph>, <codeph>~</codeph>, and <codeph>^</codeph>: Bitwise operators that return the
            logical AND, logical OR, <codeph>NOT</codeph>, or logical XOR (exclusive OR) of their argument values. Both arguments must be of
            one of the integer types. If the arguments are of different type, the argument with the smaller type is implicitly extended to
            match the argument with the longer type.
          </p>
        </li>
      </ul>

      <p>
        You can chain a sequence of arithmetic expressions, optionally grouping them with parentheses.
      </p>

      <p>
        The arithmetic operators generally do not have equivalent calling conventions using functional notation. For example, prior to
        <keyword keyref="impala22_full"/>, there is no <codeph>MOD()</codeph> function equivalent to the <codeph>%</codeph> modulo operator.
        Conversely, there are some arithmetic functions that do not have a corresponding operator. For example, for exponentiation you use
        the <codeph>POW()</codeph> function, but there is no <codeph>**</codeph> exponentiation operator. See
        <xref href="impala_math_functions.xml#math_functions"/> for the arithmetic functions you can use.
      </p>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_aggregation_explanation"/>

      <p conref="../shared/impala_common.xml#common/complex_types_aggregation_example"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

      <p rev="2.3.0">
        The following example shows how to do an arithmetic operation using a numeric field of a <codeph>STRUCT</codeph> type that is an
        item within an <codeph>ARRAY</codeph> column. Once the scalar numeric value <codeph>R_NATIONKEY</codeph> is extracted, it can be
        used in an arithmetic expression, such as multiplying by 10:
      </p>

<codeblock rev="2.3.0">
-- The SMALLINT is a field within an array of structs.
describe region;
+-------------+-------------------------+---------+
| name        | type                    | comment |
+-------------+-------------------------+---------+
| r_regionkey | smallint                |         |
| r_name      | string                  |         |
| r_comment   | string                  |         |
| r_nations   | array&lt;struct&lt;           |         |
|             |   n_nationkey:smallint, |         |
|             |   n_name:string,        |         |
|             |   n_comment:string      |         |
|             | &gt;&gt;                      |         |
+-------------+-------------------------+---------+

-- When we refer to the scalar value using dot notation,
-- we can use arithmetic and comparison operators on it
-- like any other number.
select r_name, nation.item.n_name, nation.item.n_nationkey * 10
  from region, region.r_nations as nation
where nation.item.n_nationkey &lt; 5;
+-------------+-------------+------------------------------+
| r_name      | item.n_name | nation.item.n_nationkey * 10 |
+-------------+-------------+------------------------------+
| AMERICA     | CANADA      | 30                           |
| AMERICA     | BRAZIL      | 20                           |
| AMERICA     | ARGENTINA   | 10                           |
| MIDDLE EAST | EGYPT       | 40                           |
| AFRICA      | ALGERIA     | 0                            |
+-------------+-------------+------------------------------+
</codeblock>

    </conbody>

  </concept>

  <concept id="between">

    <title>BETWEEN Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">BETWEEN operator</indexterm>
        In a <codeph>WHERE</codeph> clause, compares an expression to both a lower and upper bound. The comparison is successful is the
        expression is greater than or equal to the lower bound, and less than or equal to the upper bound. If the bound values are switched,
        so the lower bound is greater than the upper bound, does not match any values.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>expression</varname> BETWEEN <varname>lower_bound</varname> AND <varname>upper_bound</varname></codeblock>

      <p>
        <b>Data types:</b> Typically used with numeric data types. Works with any data type, although not very practical for
        <codeph>BOOLEAN</codeph> values. (<codeph>BETWEEN false AND true</codeph> will match all <codeph>BOOLEAN</codeph> values.) Use
        <codeph>CAST()</codeph> if necessary to ensure the lower and upper bound values are compatible types. Call string or date/time
        functions if necessary to extract or transform the relevant portion to compare, especially if the value can be transformed into a
        number.
      </p>

      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

      <p>
        Be careful when using short string operands. A longer string that starts with the upper bound value will not be included, because it
        is considered greater than the upper bound. For example, <codeph>BETWEEN 'A' and 'M'</codeph> would not match the string value
        <codeph>'Midway'</codeph>. Use functions such as <codeph>upper()</codeph>, <codeph>lower()</codeph>, <codeph>substr()</codeph>,
        <codeph>trim()</codeph>, and so on if necessary to ensure the comparison works as expected.
      </p>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

<codeblock>-- Retrieve data for January through June, inclusive.
select c1 from t1 where month <b>between 1 and 6</b>;

-- Retrieve data for names beginning with 'A' through 'M' inclusive.
-- Only test the first letter to ensure all the values starting with 'M' are matched.
-- Do a case-insensitive comparison to match names with various capitalization conventions.
select last_name from customers where upper(substr(last_name,1,1)) <b>between 'A' and 'M'</b>;

-- Retrieve data for only the first week of each month.
select count(distinct visitor_id)) from web_traffic where dayofmonth(when_viewed) <b>between 1 and 7</b>;</codeblock>

      <p rev="2.3.0">
        The following example shows how to do a <codeph>BETWEEN</codeph> comparison using a numeric field of a <codeph>STRUCT</codeph> type
        that is an item within an <codeph>ARRAY</codeph> column. Once the scalar numeric value <codeph>R_NATIONKEY</codeph> is extracted, it
        can be used in a comparison operator:
      </p>

<codeblock rev="2.3.0">
-- The SMALLINT is a field within an array of structs.
describe region;
+-------------+-------------------------+---------+
| name        | type                    | comment |
+-------------+-------------------------+---------+
| r_regionkey | smallint                |         |
| r_name      | string                  |         |
| r_comment   | string                  |         |
| r_nations   | array&lt;struct&lt;           |         |
|             |   n_nationkey:smallint, |         |
|             |   n_name:string,        |         |
|             |   n_comment:string      |         |
|             | &gt;&gt;                      |         |
+-------------+-------------------------+---------+

-- When we refer to the scalar value using dot notation,
-- we can use arithmetic and comparison operators on it
-- like any other number.
select r_name, nation.item.n_name, nation.item.n_nationkey
from region, region.r_nations as nation
where nation.item.n_nationkey between 3 and 5
+-------------+-------------+------------------+
| r_name      | item.n_name | item.n_nationkey |
+-------------+-------------+------------------+
| AMERICA     | CANADA      | 3                |
| MIDDLE EAST | EGYPT       | 4                |
| AFRICA      | ETHIOPIA    | 5                |
+-------------+-------------+------------------+
</codeblock>

    </conbody>

  </concept>

  <concept id="comparison_operators">

    <title>Comparison Operators</title>

    <conbody>

      <p>
        <indexterm audience="hidden">comparison operators</indexterm>
        Impala supports the familiar comparison operators for checking equality and sort order for the column data types:
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>left_hand_expression</varname> <varname>comparison_operator</varname> <varname>right_hand_expression</varname></codeblock>

      <ul>
        <li>
          <codeph>=</codeph>, <codeph>!=</codeph>, <codeph>&lt;&gt;</codeph>: apply to all types.
        </li>

        <li>
          <codeph>&lt;</codeph>, <codeph>&lt;=</codeph>, <codeph>&gt;</codeph>, <codeph>&gt;=</codeph>: apply to all types; for
          <codeph>BOOLEAN</codeph>, <codeph>TRUE</codeph> is considered greater than <codeph>FALSE</codeph>.
        </li>
      </ul>

      <p>
        <b>Alternatives:</b>
      </p>

      <p>
        The <codeph>IN</codeph> and <codeph>BETWEEN</codeph> operators provide shorthand notation for expressing combinations of equality,
        less than, and greater than comparisons with a single operator.
      </p>

      <p>
        Because comparing any value to <codeph>NULL</codeph> produces <codeph>NULL</codeph> rather than <codeph>TRUE</codeph> or
        <codeph>FALSE</codeph>, use the <codeph>IS NULL</codeph> and <codeph>IS NOT NULL</codeph> operators to check if a value is
        <codeph>NULL</codeph> or not.
      </p>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

      <p rev="2.3.0">
        The following example shows how to do an arithmetic operation using a numeric field of a <codeph>STRUCT</codeph> type that is an
        item within an <codeph>ARRAY</codeph> column. Once the scalar numeric value <codeph>R_NATIONKEY</codeph> is extracted, it can be
        used with a comparison operator such as <codeph>&lt;</codeph>:
      </p>

<codeblock rev="2.3.0">
-- The SMALLINT is a field within an array of structs.
describe region;
+-------------+-------------------------+---------+
| name        | type                    | comment |
+-------------+-------------------------+---------+
| r_regionkey | smallint                |         |
| r_name      | string                  |         |
| r_comment   | string                  |         |
| r_nations   | array&lt;struct&lt;           |         |
|             |   n_nationkey:smallint, |         |
|             |   n_name:string,        |         |
|             |   n_comment:string      |         |
|             | &gt;&gt;                      |         |
+-------------+-------------------------+---------+

-- When we refer to the scalar value using dot notation,
-- we can use arithmetic and comparison operators on it
-- like any other number.
select r_name, nation.item.n_name, nation.item.n_nationkey
from region, region.r_nations as nation
where nation.item.n_nationkey &lt; 5
+-------------+-------------+------------------+
| r_name      | item.n_name | item.n_nationkey |
+-------------+-------------+------------------+
| AMERICA     | CANADA      | 3                |
| AMERICA     | BRAZIL      | 2                |
| AMERICA     | ARGENTINA   | 1                |
| MIDDLE EAST | EGYPT       | 4                |
| AFRICA      | ALGERIA     | 0                |
+-------------+-------------+------------------+
</codeblock>

    </conbody>

  </concept>

  <concept audience="hidden" rev="2.1.0" id="except">

    <title>EXCEPT Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">EXCEPT operator</indexterm>
      </p>

    </conbody>

  </concept>

  <concept rev="2.0.0" id="exists">

    <title>EXISTS Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">EXISTS operator</indexterm>

        <indexterm audience="hidden">NOT EXISTS operator</indexterm>
        The <codeph>EXISTS</codeph> operator tests whether a subquery returns any results. You typically use it to find values from one
        table that have corresponding values in another table.
      </p>

      <p>
        The converse, <codeph>NOT EXISTS</codeph>, helps to find all the values from one table that do not have any corresponding values in
        another table.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock>EXISTS (<varname>subquery</varname>)
NOT EXISTS (<varname>subquery</varname>)
</codeblock>

      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

      <p>
        The subquery can refer to a different table than the outer query block, or the same table. For example, you might use
        <codeph>EXISTS</codeph> or <codeph>NOT EXISTS</codeph> to check the existence of parent/child relationships between two columns of
        the same table.
      </p>

      <p>
        You can also use operators and function calls within the subquery to test for other kinds of relationships other than strict
        equality. For example, you might use a call to <codeph>COUNT()</codeph> in the subquery to check whether the number of matching
        values is higher or lower than some limit. You might call a UDF in the subquery to check whether values in one table matches a
        hashed representation of those same values in a different table.
      </p>

      <p conref="../shared/impala_common.xml#common/null_blurb"/>

      <p>
        If the subquery returns any value at all (even <codeph>NULL</codeph>), <codeph>EXISTS</codeph> returns <codeph>TRUE</codeph> and
        <codeph>NOT EXISTS</codeph> returns false.
      </p>

      <p>
        The following example shows how even when the subquery returns only <codeph>NULL</codeph> values, <codeph>EXISTS</codeph> still
        returns <codeph>TRUE</codeph> and thus matches all the rows from the table in the outer query block.
      </p>

<codeblock>[localhost:21000] &gt; create table all_nulls (x int);
[localhost:21000] &gt; insert into all_nulls values (null), (null), (null);
[localhost:21000] &gt; select y from t2 where exists (select x from all_nulls);
+---+
| y |
+---+
| 2 |
| 4 |
| 6 |
+---+
</codeblock>

      <p>
        However, if the table in the subquery is empty and so the subquery returns an empty result set, <codeph>EXISTS</codeph> returns
        <codeph>FALSE</codeph>:
      </p>

<codeblock>[localhost:21000] &gt; create table empty (x int);
[localhost:21000] &gt; select y from t2 where exists (select x from empty);
[localhost:21000] &gt;
</codeblock>

      <p conref="../shared/impala_common.xml#common/added_in_20"/>

      <p conref="../shared/impala_common.xml#common/restrictions_blurb"/>

      <p conref="../shared/impala_common.xml#common/subquery_no_limit"/>

      <p rev="IMPALA-3232">
        Prior to <keyword keyref="impala26_full"/>,
        the <codeph>NOT EXISTS</codeph> operator required a correlated subquery.
        In <keyword keyref="impala26_full"/> and higher, <codeph>NOT EXISTS</codeph> works with
        uncorrelated queries also.
      </p>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

<!-- To do: construct an EXISTS / NOT EXISTS example for complex types. -->

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

      <p>
<!-- Maybe turn this into a conref if the same set of tables gets used for subqueries, EXISTS, other places. -->
<!-- Yes, the material was reused under Subqueries for anti-joins. -->
        The following examples refer to these simple tables containing small sets of integers or strings:
<codeblock>[localhost:21000] &gt; create table t1 (x int);
[localhost:21000] &gt; insert into t1 values (1), (2), (3), (4), (5), (6);

[localhost:21000] &gt; create table t2 (y int);
[localhost:21000] &gt; insert into t2 values (2), (4), (6);

[localhost:21000] &gt; create table t3 (z int);
[localhost:21000] &gt; insert into t3 values (1), (3), (5);

[localhost:21000] &gt; create table month_names (m string);
[localhost:21000] &gt; insert into month_names values
                  &gt; ('January'), ('February'), ('March'),
                  &gt; ('April'), ('May'), ('June'), ('July'),
                  &gt; ('August'), ('September'), ('October'),
                  &gt; ('November'), ('December');
</codeblock>
      </p>

      <p>
        The following example shows a correlated subquery that finds all the values in one table that exist in another table. For each value
        <codeph>X</codeph> from <codeph>T1</codeph>, the query checks if the <codeph>Y</codeph> column of <codeph>T2</codeph> contains an
        identical value, and the <codeph>EXISTS</codeph> operator returns <codeph>TRUE</codeph> or <codeph>FALSE</codeph> as appropriate in
        each case.
      </p>

<codeblock>localhost:21000] &gt; select x from t1 where exists (select y from t2 where t1.x = y);
+---+
| x |
+---+
| 2 |
| 4 |
| 6 |
+---+
</codeblock>

      <p>
        An uncorrelated query is less interesting in this case. Because the subquery always returns <codeph>TRUE</codeph>, all rows from
        <codeph>T1</codeph> are returned. If the table contents where changed so that the subquery did not match any rows, none of the rows
        from <codeph>T1</codeph> would be returned.
      </p>

<codeblock>[localhost:21000] &gt; select x from t1 where exists (select y from t2 where y &gt; 5);
+---+
| x |
+---+
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
+---+
</codeblock>

      <p>
        The following example shows how an uncorrelated subquery can test for the existence of some condition within a table. By using
        <codeph>LIMIT 1</codeph> or an aggregate function, the query returns a single result or no result based on whether the subquery
        matches any rows. Here, we know that <codeph>T1</codeph> and <codeph>T2</codeph> contain some even numbers, but <codeph>T3</codeph>
        does not.
      </p>

<codeblock>[localhost:21000] &gt; select "contains an even number" from t1 where exists (select x from t1 where x % 2 = 0) limit 1;
+---------------------------+
| 'contains an even number' |
+---------------------------+
| contains an even number   |
+---------------------------+
[localhost:21000] &gt; select "contains an even number" as assertion from t1 where exists (select x from t1 where x % 2 = 0) limit 1;
+-------------------------+
| assertion               |
+-------------------------+
| contains an even number |
+-------------------------+
[localhost:21000] &gt; select "contains an even number" as assertion from t2 where exists (select x from t2 where y % 2 = 0) limit 1;
ERROR: AnalysisException: couldn't resolve column reference: 'x'
[localhost:21000] &gt; select "contains an even number" as assertion from t2 where exists (select y from t2 where y % 2 = 0) limit 1;
+-------------------------+
| assertion               |
+-------------------------+
| contains an even number |
+-------------------------+
[localhost:21000] &gt; select "contains an even number" as assertion from t3 where exists (select z from t3 where z % 2 = 0) limit 1;
[localhost:21000] &gt;
</codeblock>

      <p>
        The following example finds numbers in one table that are 1 greater than numbers from another table. The <codeph>EXISTS</codeph>
        notation is simpler than an equivalent <codeph>CROSS JOIN</codeph> between the tables. (The example then also illustrates how the
        same test could be performed using an <codeph>IN</codeph> operator.)
      </p>

<codeblock>[localhost:21000] &gt; select x from t1 where exists (select y from t2 where x = y + 1);
+---+
| x |
+---+
| 3 |
| 5 |
+---+
[localhost:21000] &gt; select x from t1 where x in (select y + 1 from t2);
+---+
| x |
+---+
| 3 |
| 5 |
+---+
</codeblock>

      <p>
        The following example finds values from one table that do not exist in another table.
      </p>

<codeblock>[localhost:21000] &gt; select x from t1 where not exists (select y from t2 where x = y);
+---+
| x |
+---+
| 1 |
| 3 |
| 5 |
+---+
</codeblock>

      <p>
        The following example uses the <codeph>NOT EXISTS</codeph> operator to find all the leaf nodes in tree-structured data. This
        simplified <q>tree of life</q> has multiple levels (class, order, family, and so on), with each item pointing upward through a
        <codeph>PARENT</codeph> pointer. The example runs an outer query and a subquery on the same table, returning only those items whose
        <codeph>ID</codeph> value is <i>not</i> referenced by the <codeph>PARENT</codeph> of any other item.
      </p>

<codeblock>[localhost:21000] &gt; create table tree (id int, parent int, name string);
[localhost:21000] &gt; insert overwrite tree values
                  &gt; (0, null, "animals"),
                  &gt; (1, 0, "placentals"),
                  &gt; (2, 0, "marsupials"),
                  &gt; (3, 1, "bats"),
                  &gt; (4, 1, "cats"),
                  &gt; (5, 2, "kangaroos"),
                  &gt; (6, 4, "lions"),
                  &gt; (7, 4, "tigers"),
                  &gt; (8, 5, "red kangaroo"),
                  &gt; (9, 2, "wallabies");
[localhost:21000] &gt; select name as "leaf node" from tree one
                  &gt; where not exists (select parent from tree two where one.id = two.parent);
+--------------+
| leaf node    |
+--------------+
| bats         |
| lions        |
| tigers       |
| red kangaroo |
| wallabies    |
+--------------+
</codeblock>

      <p conref="../shared/impala_common.xml#common/related_info"/>

      <p>
        <xref href="impala_subqueries.xml#subqueries"/>
      </p>

    </conbody>

  </concept>

  <concept rev="2.4.0" id="ilike">

    <title>ILIKE Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">ILIKE operator</indexterm>
        A case-insensitive comparison operator for <codeph>STRING</codeph> data, with basic wildcard capability using <codeph>_</codeph> to match a single
        character and <codeph>%</codeph> to match multiple characters. The argument expression must match the entire string value.
        Typically, it is more efficient to put any <codeph>%</codeph> wildcard match at the end of the string.
      </p>

      <p>
        This operator, available in <keyword keyref="impala25_full"/> and higher, is the equivalent of the <codeph>LIKE</codeph> operator,
        but with case-insensitive comparisons.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>string_expression</varname> ILIKE <varname>wildcard_expression</varname>
<varname>string_expression</varname> NOT ILIKE <varname>wildcard_expression</varname>
</codeblock>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

<!-- To do: construct a LIKE example for complex types. -->

      <p conref="../shared/impala_common.xml#common/example_blurb"/>
      <p>
        In the following examples, strings that are the same except for differences in uppercase
        and lowercase match successfully with <codeph>ILIKE</codeph>, but do not match
        with <codeph>LIKE</codeph>:
      </p>

<codeblock>select 'fooBar' ilike 'FOOBAR';
+-------------------------+
| 'foobar' ilike 'foobar' |
+-------------------------+
| true                    |
+-------------------------+

select 'fooBar' like 'FOOBAR';
+------------------------+
| 'foobar' like 'foobar' |
+------------------------+
| false                  |
+------------------------+

select 'FOOBAR' ilike 'f%';
+---------------------+
| 'foobar' ilike 'f%' |
+---------------------+
| true                |
+---------------------+

select 'FOOBAR' like 'f%';
+--------------------+
| 'foobar' like 'f%' |
+--------------------+
| false              |
+--------------------+

select 'ABCXYZ' not ilike 'ab_xyz';
+-----------------------------+
| not 'abcxyz' ilike 'ab_xyz' |
+-----------------------------+
| false                       |
+-----------------------------+

select 'ABCXYZ' not like 'ab_xyz';
+----------------------------+
| not 'abcxyz' like 'ab_xyz' |
+----------------------------+
| true                       |
+----------------------------+
</codeblock>

      <p conref="../shared/impala_common.xml#common/related_info"/>

      <p rev="2.5.0">
        For case-sensitive comparisons, see <xref href="impala_operators.xml#like"/>.
        For a more general kind of search operator using regular expressions, see <xref href="impala_operators.xml#regexp"/>
        or its case-insensitive counterpart <xref href="impala_operators.xml#iregexp"/>.
      </p>

    </conbody>

  </concept>

  <concept id="in">

    <title>IN Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">IN operator</indexterm>

        <indexterm audience="hidden">NOT IN operator</indexterm>
        The <codeph>IN</codeph> operator compares an argument value to a set of values, and returns <codeph>TRUE</codeph> if the argument
        matches any value in the set. The <codeph>NOT IN</codeph> operator reverses the comparison, and checks if the argument value is not
        part of a set of values.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock rev="2.0.0"><varname>expression</varname> IN (<varname>expression</varname> [, <varname>expression</varname>])
<varname>expression</varname> IN (<varname>subquery</varname>)

<varname>expression</varname> NOT IN (<varname>expression</varname> [, <varname>expression</varname>])
<varname>expression</varname> NOT IN (<varname>subquery</varname>)
</codeblock>

      <p>
        The left-hand expression and the set of comparison values must be of compatible types.
      </p>

      <p>
        The left-hand expression must consist only of a single value, not a tuple. Although the left-hand expression is typically a column
        name, it could also be some other value. For example, the <codeph>WHERE</codeph> clauses <codeph>WHERE id IN (5)</codeph> and
        <codeph>WHERE 5 IN (id)</codeph> produce the same results.
      </p>

      <p rev="">
        The set of values to check against can be specified as constants, function calls, column names, or other expressions in the query
        text. The maximum number of expressions in the <codeph>IN</codeph> list is 9999. (The maximum number of elements of
        a single expression is 10,000 items, and the <codeph>IN</codeph> operator itself counts as one.)
      </p>

      <p rev="2.0.0">
        In Impala 2.0 and higher, the set of values can also be generated by a subquery. <codeph>IN</codeph> can evaluate an unlimited
        number of results using a subquery.
      </p>

      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

      <p>
        Any expression using the <codeph>IN</codeph> operator could be rewritten as a series of equality tests connected with
        <codeph>OR</codeph>, but the <codeph>IN</codeph> syntax is often clearer, more concise, and easier for Impala to optimize. For
        example, with partitioned tables, queries frequently use <codeph>IN</codeph> clauses to filter data by comparing the partition key
        columns to specific values.
      </p>

      <p conref="../shared/impala_common.xml#common/null_blurb"/>

      <p>
        If there really is a matching non-null value, <codeph>IN</codeph> returns <codeph>TRUE</codeph>:
      </p>

<codeblock>[localhost:21000] &gt; select 1 in (1,null,2,3);
+----------------------+
| 1 in (1, null, 2, 3) |
+----------------------+
| true                 |
+----------------------+
[localhost:21000] &gt; select 1 not in (1,null,2,3);
+--------------------------+
| 1 not in (1, null, 2, 3) |
+--------------------------+
| false                    |
+--------------------------+
</codeblock>

      <p>
        If the searched value is not found in the comparison values, and the comparison values include <codeph>NULL</codeph>, the result is
        <codeph>NULL</codeph>:
      </p>

<codeblock>[localhost:21000] &gt; select 5 in (1,null,2,3);
+----------------------+
| 5 in (1, null, 2, 3) |
+----------------------+
| NULL                 |
+----------------------+
[localhost:21000] &gt; select 5 not in (1,null,2,3);
+--------------------------+
| 5 not in (1, null, 2, 3) |
+--------------------------+
| NULL                     |
+--------------------------+
[localhost:21000] &gt; select 1 in (null);
+-------------+
| 1 in (null) |
+-------------+
| NULL        |
+-------------+
[localhost:21000] &gt; select 1 not in (null);
+-----------------+
| 1 not in (null) |
+-----------------+
| NULL            |
+-----------------+
</codeblock>

      <p>
        If the left-hand argument is <codeph>NULL</codeph>, <codeph>IN</codeph> always returns <codeph>NULL</codeph>. This rule applies even
        if the comparison values include <codeph>NULL</codeph>.
      </p>

<codeblock>[localhost:21000] &gt; select null in (1,2,3);
+-------------------+
| null in (1, 2, 3) |
+-------------------+
| NULL              |
+-------------------+
[localhost:21000] &gt; select null not in (1,2,3);
+-----------------------+
| null not in (1, 2, 3) |
+-----------------------+
| NULL                  |
+-----------------------+
[localhost:21000] &gt; select null in (null);
+----------------+
| null in (null) |
+----------------+
| NULL           |
+----------------+
[localhost:21000] &gt; select null not in (null);
+--------------------+
| null not in (null) |
+--------------------+
| NULL               |
+--------------------+
</codeblock>

      <p conref="../shared/impala_common.xml#common/enhanced_in_20"/>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

      <p rev="2.3.0">
        The following example shows how to do an arithmetic operation using a numeric field of a <codeph>STRUCT</codeph> type that is an
        item within an <codeph>ARRAY</codeph> column. Once the scalar numeric value <codeph>R_NATIONKEY</codeph> is extracted, it can be
        used in an arithmetic expression, such as multiplying by 10:
      </p>

<codeblock rev="2.3.0">
-- The SMALLINT is a field within an array of structs.
describe region;
+-------------+-------------------------+---------+
| name        | type                    | comment |
+-------------+-------------------------+---------+
| r_regionkey | smallint                |         |
| r_name      | string                  |         |
| r_comment   | string                  |         |
| r_nations   | array&lt;struct&lt;           |         |
|             |   n_nationkey:smallint, |         |
|             |   n_name:string,        |         |
|             |   n_comment:string      |         |
|             | &gt;&gt;                      |         |
+-------------+-------------------------+---------+

-- When we refer to the scalar value using dot notation,
-- we can use arithmetic and comparison operators on it
-- like any other number.
select r_name, nation.item.n_name, nation.item.n_nationkey
from region, region.r_nations as nation
where nation.item.n_nationkey in (1,3,5)
+---------+-------------+------------------+
| r_name  | item.n_name | item.n_nationkey |
+---------+-------------+------------------+
| AMERICA | CANADA      | 3                |
| AMERICA | ARGENTINA   | 1                |
| AFRICA  | ETHIOPIA    | 5                |
+---------+-------------+------------------+
</codeblock>

      <p conref="../shared/impala_common.xml#common/restrictions_blurb"/>

      <p conref="../shared/impala_common.xml#common/subquery_no_limit"/>

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

<codeblock>-- Using IN is concise and self-documenting.
SELECT * FROM t1 WHERE c1 IN (1,2,10);
-- Equivalent to series of = comparisons ORed together.
SELECT * FROM t1 WHERE c1 = 1 OR c1 = 2 OR c1 = 10;

SELECT c1 AS "starts with vowel" FROM t2 WHERE upper(substr(c1,1,1)) IN ('A','E','I','O','U');

SELECT COUNT(DISTINCT(visitor_id)) FROM web_traffic WHERE month IN ('January','June','July');</codeblock>

      <p conref="../shared/impala_common.xml#common/related_info"/>

      <p>
        <xref href="impala_subqueries.xml#subqueries"/>
      </p>

    </conbody>

  </concept>

  <concept audience="hidden" rev="2.1.0" id="intersect">

    <title>INTERSECT Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">INTERSECT operator</indexterm>
      </p>

    </conbody>

  </concept>

  <concept rev="2.5.0" id="iregexp">

    <title>IREGEXP Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">IREGEXP operator</indexterm>
        Tests whether a value matches a regular expression, using case-insensitive string comparisons.
        Uses the POSIX regular expression syntax where <codeph>^</codeph> and
        <codeph>$</codeph> match the beginning and end of the string, <codeph>.</codeph> represents any single character, <codeph>*</codeph>
        represents a sequence of zero or more items, <codeph>+</codeph> represents a sequence of one or more items, <codeph>?</codeph>
        produces a non-greedy match, and so on.
      </p>

      <p>
        This operator, available in <keyword keyref="impala25_full"/> and higher, is the equivalent of the <codeph>REGEXP</codeph> operator,
        but with case-insensitive comparisons.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>string_expression</varname> IREGEXP <varname>regular_expression</varname>
</codeblock>

      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

<!-- Currently, there isn't any IRLIKE synonym, so REGEXP and IREGEXP are different in that respect.
     I pinged IMPALA-1787 to check if that's intentional.
      <p>
        The <codeph>IRLIKE</codeph> operator is a synonym for <codeph>IREGEXP</codeph>.
      </p>
-->

      <p rev="2.5.0">
        The <codeph>|</codeph> symbol is the alternation operator, typically used within <codeph>()</codeph> to match different sequences.
        The <codeph>()</codeph> groups do not allow backreferences. To retrieve the part of a value matched within a <codeph>()</codeph>
        section, use the <codeph><xref href="impala_string_functions.xml#string_functions/regexp_extract">regexp_extract()</xref></codeph>
        built-in function. (Currently, there is not any case-insensitive equivalent for the <codeph>regexp_extract()</codeph> function.)
      </p>

      <p rev="1.3.1" conref="../shared/impala_common.xml#common/regexp_matching"/>

      <p conref="../shared/impala_common.xml#common/regexp_re2"/>

      <p conref="../shared/impala_common.xml#common/regexp_re2_warning"/>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

<!-- To do: construct a REGEXP example for complex types. -->

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

      <p>
        The following examples demonstrate the syntax for the <codeph>IREGEXP</codeph> operator.
      </p>

<codeblock>select 'abcABCaabbcc' iregexp '^[a-c]+$';
+---------------------------------+
| 'abcabcaabbcc' iregexp '[a-c]+' |
+---------------------------------+
| true                            |
+---------------------------------+
</codeblock>

      <p conref="../shared/impala_common.xml#common/related_info"/>

      <p>
        <xref href="impala_operators.xml#regexp"/>
      </p>

    </conbody>

  </concept>

  <concept rev="2.5.0 IMPALA-2147" id="is_distinct_from">

    <title id="is_distinct">IS DISTINCT FROM Operator</title>

    <conbody>

      <p> The <codeph>IS DISTINCT FROM</codeph> operator, and its converse the
          <codeph>IS NOT DISTINCT FROM</codeph> operator, test whether or not
        values are identical. <codeph>IS NOT DISTINCT FROM</codeph> is similar
        to the <codeph>=</codeph> operator, and <codeph>IS DISTINCT
          FROM</codeph> is similar to the <codeph>!=</codeph> operator, except
        that <codeph>NULL</codeph> values are treated as identical. Therefore,
          <codeph>IS NOT DISTINCT FROM</codeph> returns <codeph>true</codeph>
        rather than <codeph>NULL</codeph>, and <codeph>IS DISTINCT FROM</codeph>
        returns <codeph>false</codeph> rather than <codeph>NULL</codeph>, when
        comparing two <codeph>NULL</codeph> values. If one of the values being
        compared is <codeph>NULL</codeph> and the other is not, <codeph>IS
          DISTINCT FROM</codeph> returns <codeph>true</codeph> and <codeph>IS
          NOT DISTINCT FROM</codeph> returns <codeph>false</codeph>, again
        instead of returning <codeph>NULL</codeph> in both cases. </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>expression1</varname> IS DISTINCT FROM <varname>expression2</varname>

<varname>expression1</varname> IS NOT DISTINCT FROM <varname>expression2</varname>
<varname>expression1</varname> &lt;=&gt; <varname>expression2</varname>
</codeblock>

      <p>
        The operator <codeph>&lt;=&gt;</codeph> is an alias for <codeph>IS NOT DISTINCT FROM</codeph>.
        It is typically used as a <codeph>NULL</codeph>-safe equality operator in join queries.
        That is, <codeph>A &lt;=&gt; B</codeph> is true if <codeph>A</codeph> equals <codeph>B</codeph>
        or if both <codeph>A</codeph> and <codeph>B</codeph> are <codeph>NULL</codeph>.
      </p>

      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

      <p>
        This operator provides concise notation for comparing two values and always producing a <codeph>true</codeph> or
        <codeph>false</codeph> result, without treating <codeph>NULL</codeph> as a special case. Otherwise, to unambiguously distinguish
        between two values requires a compound expression involving <codeph>IS [NOT] NULL</codeph> tests of both operands in addition to the
        <codeph>=</codeph> or <codeph>!=</codeph> operator.
      </p>

      <p> The <codeph>&lt;=&gt;</codeph> operator, used like an equality
        operator in a join query, is more efficient than the equivalent clause:
          <codeph>IF (A IS NULL OR B IS NULL, A IS NULL AND B IS NULL, A =
          B)</codeph>. The <codeph>&lt;=&gt;</codeph> operator can use a hash
        join, while the <codeph>IF</codeph> expression cannot. </p>

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

      <p>
        The following examples show how <codeph>IS DISTINCT FROM</codeph> gives output similar to
        the <codeph>!=</codeph> operator, and <codeph>IS NOT DISTINCT FROM</codeph> gives output
        similar to the <codeph>=</codeph> operator. The exception is when the expression involves
        a <codeph>NULL</codeph> value on one side or both sides, where <codeph>!=</codeph> and
        <codeph>=</codeph> return <codeph>NULL</codeph> but the <codeph>IS [NOT] DISTINCT FROM</codeph>
        operators still return <codeph>true</codeph> or <codeph>false</codeph>.
      </p>

<codeblock>
select 1 is distinct from 0, 1 != 0;
+----------------------+--------+
| 1 is distinct from 0 | 1 != 0 |
+----------------------+--------+
| true                 | true   |
+----------------------+--------+

select 1 is distinct from 1, 1 != 1;
+----------------------+--------+
| 1 is distinct from 1 | 1 != 1 |
+----------------------+--------+
| false                | false  |
+----------------------+--------+

select 1 is distinct from null, 1 != null;
+-------------------------+-----------+
| 1 is distinct from null | 1 != null |
+-------------------------+-----------+
| true                    | NULL      |
+-------------------------+-----------+

select null is distinct from null, null != null;
+----------------------------+--------------+
| null is distinct from null | null != null |
+----------------------------+--------------+
| false                      | NULL         |
+----------------------------+--------------+

select 1 is not distinct from 0, 1 = 0;
+--------------------------+-------+
| 1 is not distinct from 0 | 1 = 0 |
+--------------------------+-------+
| false                    | false |
+--------------------------+-------+

select 1 is not distinct from 1, 1 = 1;
+--------------------------+-------+
| 1 is not distinct from 1 | 1 = 1 |
+--------------------------+-------+
| true                     | true  |
+--------------------------+-------+

select 1 is not distinct from null, 1 = null;
+-----------------------------+----------+
| 1 is not distinct from null | 1 = null |
+-----------------------------+----------+
| false                       | NULL     |
+-----------------------------+----------+

select null is not distinct from null, null = null;
+--------------------------------+-------------+
| null is not distinct from null | null = null |
+--------------------------------+-------------+
| true                           | NULL        |
+--------------------------------+-------------+
</codeblock>

      <p>
        The following example shows how <codeph>IS DISTINCT FROM</codeph> considers
        <codeph>CHAR</codeph> values to be the same (not distinct from each other)
        if they only differ in the number of trailing spaces. Therefore, sometimes
        the result of an <codeph>IS [NOT] DISTINCT FROM</codeph> operator differs
        depending on whether the values are <codeph>STRING</codeph>/<codeph>VARCHAR</codeph>
        or <codeph>CHAR</codeph>.
      </p>

<codeblock>
select
  'x' is distinct from 'x ' as string_with_trailing_spaces,
  cast('x' as char(5)) is distinct from cast('x ' as char(5)) as char_with_trailing_spaces;
+-----------------------------+---------------------------+
| string_with_trailing_spaces | char_with_trailing_spaces |
+-----------------------------+---------------------------+
| true                        | false                     |
+-----------------------------+---------------------------+
</codeblock>
    </conbody>

  </concept>

  <concept id="is_null">

    <title>IS NULL Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">IS NULL operator</indexterm>
        <indexterm audience="hidden">IS NOT NULL operator</indexterm>
        <indexterm audience="hidden">IS UNKNOWN operator</indexterm>
        <indexterm audience="hidden">IS NOT UNKNOWN operator</indexterm>

        The <codeph>IS NULL</codeph> operator, and its converse the <codeph>IS NOT NULL</codeph> operator, test whether a specified value is
        <codeph><xref href="impala_literals.xml#null">NULL</xref></codeph>. Because using <codeph>NULL</codeph> with any of the other
        comparison operators such as <codeph>=</codeph> or <codeph>!=</codeph> also returns <codeph>NULL</codeph> rather than
        <codeph>TRUE</codeph> or <codeph>FALSE</codeph>, you use a special-purpose comparison operator to check for this special condition.
      </p>

      <p rev="2.11.0 IMPALA-1767">
        In <keyword keyref="impala211_full"/> and higher, you can use
        the operators <codeph>IS UNKNOWN</codeph> and
        <codeph>IS NOT UNKNOWN</codeph> as synonyms for
        <codeph>IS NULL</codeph> and <codeph>IS NOT NULL</codeph>,
        respectively.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>expression</varname> IS NULL
<varname>expression</varname> IS NOT NULL

<ph rev="2.11.0 IMPALA-1767"><varname>expression</varname> IS UNKNOWN</ph>
<ph rev="2.11.0 IMPALA-1767"><varname>expression</varname> IS NOT UNKNOWN</ph>
</codeblock>

      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

      <p>
        In many cases, <codeph>NULL</codeph> values indicate some incorrect or incomplete processing during data ingestion or conversion.
        You might check whether any values in a column are <codeph>NULL</codeph>, and if so take some followup action to fill them in.
      </p>

      <p>
        With sparse data, often represented in <q>wide</q> tables, it is common for most values to be <codeph>NULL</codeph> with only an
        occasional non-<codeph>NULL</codeph> value. In those cases, you can use the <codeph>IS NOT NULL</codeph> operator to identify the
        rows containing any data at all for a particular column, regardless of the actual value.
      </p>

      <p>
        With a well-designed database schema, effective use of <codeph>NULL</codeph> values and <codeph>IS NULL</codeph> and <codeph>IS NOT
        NULL</codeph> operators can save having to design custom logic around special values such as 0, -1, <codeph>'N/A'</codeph>, empty
        string, and so on. <codeph>NULL</codeph> lets you distinguish between a value that is known to be 0, false, or empty, and a truly
        unknown value.
      </p>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p rev="2.3.0">
        The <codeph>IS [NOT] UNKNOWN</codeph> operator, as with the <codeph>IS [NOT] NULL</codeph>
        operator, is not applicable to complex type columns (<codeph>STRUCT</codeph>,
        <codeph>ARRAY</codeph>, or <codeph>MAP</codeph>). Using a complex type column with this
        operator causes a query error.
      </p>

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

<codeblock>-- If this value is non-zero, something is wrong.
select count(*) from employees where employee_id is null;

-- With data from disparate sources, some fields might be blank.
-- Not necessarily an error condition.
select count(*) from census where household_income is null;

-- Sometimes we expect fields to be null, and followup action
-- is needed when they are not.
select count(*) from web_traffic where weird_http_code is not null;</codeblock>

    </conbody>

  </concept>

  <concept id="is_true" rev="2.11.0 IMPALA-1767">

    <title>IS TRUE Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">IS TRUE operator</indexterm>
        <indexterm audience="hidden">IS FALSE operator</indexterm>
        <indexterm audience="hidden">IS NOT TRUE operator</indexterm>
        <indexterm audience="hidden">IS NOT FALSE operator</indexterm>
        This variation of the <codeph>IS</codeph> operator tests for truth
        or falsity, with right-hand arguments <codeph>[NOT] TRUE</codeph>,
        <codeph>[NOT] FALSE</codeph>, and <codeph>[NOT] UNKNOWN</codeph>.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>expression</varname> IS TRUE
<varname>expression</varname> IS NOT TRUE

<varname>expression</varname> IS FALSE
<varname>expression</varname> IS NOT FALSE

</codeblock>

      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

      <p>
        This <codeph>IS TRUE</codeph> and <codeph>IS FALSE</codeph> forms are
        similar to doing equality comparisons with the Boolean values
        <codeph>TRUE</codeph> and <codeph>FALSE</codeph>, except that
        <codeph>IS TRUE</codeph> and <codeph>IS FALSE</codeph>
        always return either <codeph>TRUE</codeph> or <codeph>FALSE</codeph>,
        even if the left-hand side expression returns <codeph>NULL</codeph>
      </p>

      <p rev="2.11.0 IMPALA-1767">
        These operators let you simplify Boolean comparisons that must also
        check for <codeph>NULL</codeph>, for example
        <codeph>X != 10 AND X IS NOT NULL</codeph> is equivalent to
        <codeph>(X != 10) IS TRUE</codeph>.
      </p>

      <p conref="../shared/impala_common.xml#common/boolean_functions_vs_expressions"/>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p rev="2.3.0">
        The <codeph>IS [NOT] TRUE</codeph> and <codeph>IS [NOT] FALSE</codeph> operators are not
        applicable to complex type columns (<codeph>STRUCT</codeph>, <codeph>ARRAY</codeph>, or
        <codeph>MAP</codeph>). Using a complex type column with these operators causes a query error.
      </p>

      <p conref="../shared/impala_common.xml#common/added_in_2110"/>

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

<codeblock>
select assertion, b, b is true, b is false, b is unknown
  from boolean_test;
+-------------+-------+-----------+------------+-----------+
| assertion   | b     | istrue(b) | isfalse(b) | b is null |
+-------------+-------+-----------+------------+-----------+
| 2 + 2 = 4   | true  | true      | false      | false     |
| 2 + 2 = 5   | false | false     | true       | false     |
| 1 = null    | NULL  | false     | false      | true      |
| null = null | NULL  | false     | false      | true      |
+-------------+-------+-----------+------------+-----------+
</codeblock>

    </conbody>

  </concept>

  <concept id="like">

    <title>LIKE Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">LIKE operator</indexterm>
        A comparison operator for <codeph>STRING</codeph> data, with basic wildcard capability using the underscore
        (<codeph>_</codeph>) to match a single character and the percent sign (<codeph>%</codeph>) to match multiple
        characters. The argument expression must match the entire string value.
        Typically, it is more efficient to put any <codeph>%</codeph> wildcard match at the end of the string.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>string_expression</varname> LIKE <varname>wildcard_expression</varname>
<varname>string_expression</varname> NOT LIKE <varname>wildcard_expression</varname>
</codeblock>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

<!-- To do: construct a LIKE example for complex types. -->

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

<codeblock>select distinct c_last_name from customer where c_last_name like 'Mc%' or c_last_name like 'Mac%';
select count(c_last_name) from customer where c_last_name like 'M%';
select c_email_address from customer where c_email_address like '%.edu';

-- We can find 4-letter names beginning with 'M' by calling functions...
select distinct c_last_name from customer where length(c_last_name) = 4 and substr(c_last_name,1,1) = 'M';
-- ...or in a more readable way by matching M followed by exactly 3 characters.
select distinct c_last_name from customer where c_last_name like 'M___';</codeblock>

      <p rev="2.5.0">
        For case-insensitive comparisons, see <xref href="impala_operators.xml#ilike"/>.
        For a more general kind of search operator using regular expressions, see <xref href="impala_operators.xml#regexp"/>
        or its case-insensitive counterpart <xref href="impala_operators.xml#iregexp"/>.
      </p>

    </conbody>

  </concept>

  <concept id="logical_operators">

    <title>Logical Operators</title>

    <conbody>

      <p>
        <indexterm audience="hidden">logical operators</indexterm>
        Logical operators return a <codeph>BOOLEAN</codeph> value, based on a binary or unary logical operation between arguments that are
        also Booleans. Typically, the argument expressions use <xref href="impala_operators.xml#comparison_operators">comparison
        operators</xref>.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>boolean_expression</varname> <varname>binary_logical_operator</varname> <varname>boolean_expression</varname>
<varname>unary_logical_operator</varname> <varname>boolean_expression</varname>
</codeblock>

      <p>
        The Impala logical operators are:
      </p>

      <ul>
        <li>
          <codeph>AND</codeph>: A binary operator that returns <codeph>true</codeph> if its left-hand and right-hand arguments both evaluate
          to <codeph>true</codeph>, <codeph>NULL</codeph> if either argument is <codeph>NULL</codeph>, and <codeph>false</codeph> otherwise.
        </li>

        <li>
          <codeph>OR</codeph>: A binary operator that returns <codeph>true</codeph> if either of its left-hand and right-hand arguments
          evaluate to <codeph>true</codeph>, <codeph>NULL</codeph> if one argument is <codeph>NULL</codeph> and the other is either
          <codeph>NULL</codeph> or <codeph>false</codeph>, and <codeph>false</codeph> otherwise.
        </li>

        <li>
          <codeph>NOT</codeph>: A unary operator that flips the state of a Boolean expression from <codeph>true</codeph> to
          <codeph>false</codeph>, or <codeph>false</codeph> to <codeph>true</codeph>. If the argument expression is <codeph>NULL</codeph>,
          the result remains <codeph>NULL</codeph>. (When <codeph>NOT</codeph> is used this way as a unary logical operator, it works
          differently than the <codeph>IS NOT NULL</codeph> comparison operator, which returns <codeph>true</codeph> when applied to a
          <codeph>NULL</codeph>.)
        </li>
      </ul>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

      <p rev="2.3.0">
        The following example shows how to do an arithmetic operation using a numeric field of a <codeph>STRUCT</codeph> type that is an
        item within an <codeph>ARRAY</codeph> column. Once the scalar numeric value <codeph>R_NATIONKEY</codeph> is extracted, it can be
        used in an arithmetic expression, such as multiplying by 10:
      </p>

<codeblock rev="2.3.0">
-- The SMALLINT is a field within an array of structs.
describe region;
+-------------+-------------------------+---------+
| name        | type                    | comment |
+-------------+-------------------------+---------+
| r_regionkey | smallint                |         |
| r_name      | string                  |         |
| r_comment   | string                  |         |
| r_nations   | array&lt;struct&lt;           |         |
|             |   n_nationkey:smallint, |         |
|             |   n_name:string,        |         |
|             |   n_comment:string      |         |
|             | &gt;&gt;                      |         |
+-------------+-------------------------+---------+

-- When we refer to the scalar value using dot notation,
-- we can use arithmetic and comparison operators on it
-- like any other number.
select r_name, nation.item.n_name, nation.item.n_nationkey
  from region, region.r_nations as nation
where
  nation.item.n_nationkey between 3 and 5
  or nation.item.n_nationkey &lt; 15;
+-------------+----------------+------------------+
| r_name      | item.n_name    | item.n_nationkey |
+-------------+----------------+------------------+
| EUROPE      | UNITED KINGDOM | 23               |
| EUROPE      | RUSSIA         | 22               |
| EUROPE      | ROMANIA        | 19               |
| ASIA        | VIETNAM        | 21               |
| ASIA        | CHINA          | 18               |
| AMERICA     | UNITED STATES  | 24               |
| AMERICA     | PERU           | 17               |
| AMERICA     | CANADA         | 3                |
| MIDDLE EAST | SAUDI ARABIA   | 20               |
| MIDDLE EAST | EGYPT          | 4                |
| AFRICA      | MOZAMBIQUE     | 16               |
| AFRICA      | ETHIOPIA       | 5                |
+-------------+----------------+------------------+
</codeblock>

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

      <p>
        These examples demonstrate the <codeph>AND</codeph> operator:
      </p>

<codeblock>[localhost:21000] &gt; select true and true;
+---------------+
| true and true |
+---------------+
| true          |
+---------------+
[localhost:21000] &gt; select true and false;
+----------------+
| true and false |
+----------------+
| false          |
+----------------+
[localhost:21000] &gt; select false and false;
+-----------------+
| false and false |
+-----------------+
| false           |
+-----------------+
[localhost:21000] &gt; select true and null;
+---------------+
| true and null |
+---------------+
| NULL          |
+---------------+
[localhost:21000] &gt; select (10 &gt; 2) and (6 != 9);
+-----------------------+
| (10 &gt; 2) and (6 != 9) |
+-----------------------+
| true                  |
+-----------------------+
</codeblock>

      <p>
        These examples demonstrate the <codeph>OR</codeph> operator:
      </p>

<codeblock>[localhost:21000] &gt; select true or true;
+--------------+
| true or true |
+--------------+
| true         |
+--------------+
[localhost:21000] &gt; select true or false;
+---------------+
| true or false |
+---------------+
| true          |
+---------------+
[localhost:21000] &gt; select false or false;
+----------------+
| false or false |
+----------------+
| false          |
+----------------+
[localhost:21000] &gt; select true or null;
+--------------+
| true or null |
+--------------+
| true         |
+--------------+
[localhost:21000] &gt; select null or true;
+--------------+
| null or true |
+--------------+
| true         |
+--------------+
[localhost:21000] &gt; select false or null;
+---------------+
| false or null |
+---------------+
| NULL          |
+---------------+
[localhost:21000] &gt; select (1 = 1) or ('hello' = 'world');
+--------------------------------+
| (1 = 1) or ('hello' = 'world') |
+--------------------------------+
| true                           |
+--------------------------------+
[localhost:21000] &gt; select (2 + 2 != 4) or (-1 &gt; 0);
+--------------------------+
| (2 + 2 != 4) or (-1 &gt; 0) |
+--------------------------+
| false                    |
+--------------------------+
</codeblock>

      <p>
        These examples demonstrate the <codeph>NOT</codeph> operator:
      </p>

<codeblock>[localhost:21000] &gt; select not true;
+----------+
| not true |
+----------+
| false    |
+----------+
[localhost:21000] &gt; select not false;
+-----------+
| not false |
+-----------+
| true      |
+-----------+
[localhost:21000] &gt; select not null;
+----------+
| not null |
+----------+
| NULL     |
+----------+
[localhost:21000] &gt; select not (1=1);
+-------------+
| not (1 = 1) |
+-------------+
| false       |
+-------------+
</codeblock>

    </conbody>

  </concept>

  <concept id="regexp">

    <title>REGEXP Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">REGEXP operator</indexterm>
        Tests whether a value matches a regular expression. Uses the POSIX regular expression syntax where <codeph>^</codeph> and
        <codeph>$</codeph> match the beginning and end of the string, <codeph>.</codeph> represents any single character, <codeph>*</codeph>
        represents a sequence of zero or more items, <codeph>+</codeph> represents a sequence of one or more items, <codeph>?</codeph>
        produces a non-greedy match, and so on.
      </p>

      <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

<codeblock><varname>string_expression</varname> REGEXP <varname>regular_expression</varname>
</codeblock>

      <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

      <p>
        The <codeph>RLIKE</codeph> operator is a synonym for <codeph>REGEXP</codeph>.
      </p>

      <p>
        The <codeph>|</codeph> symbol is the alternation operator, typically used within <codeph>()</codeph> to match different sequences.
        The <codeph>()</codeph> groups do not allow backreferences. To retrieve the part of a value matched within a <codeph>()</codeph>
        section, use the <codeph><xref href="impala_string_functions.xml#string_functions/regexp_extract">regexp_extract()</xref></codeph>
        built-in function.
      </p>

      <p rev="1.3.1" conref="../shared/impala_common.xml#common/regexp_matching"/>

      <p conref="../shared/impala_common.xml#common/regexp_re2"/>

      <p conref="../shared/impala_common.xml#common/regexp_re2_warning"/>

      <p conref="../shared/impala_common.xml#common/complex_types_blurb"/>

      <p conref="../shared/impala_common.xml#common/complex_types_caveat_no_operator"/>

<!-- To do: construct a REGEXP example for complex types. -->

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

      <p>
        The following examples demonstrate the identical syntax for the <codeph>REGEXP</codeph> and <codeph>RLIKE</codeph> operators.
      </p>

<!-- Same examples shown for both REGEXP and RLIKE operators. -->

<codeblock conref="../shared/impala_common.xml#common/regexp_rlike_examples"/>

      <p conref="../shared/impala_common.xml#common/related_info"/>

      <p rev="2.5.0">
        For regular expression matching with case-insensitive comparisons, see <xref href="impala_operators.xml#iregexp"/>.
      </p>

    </conbody>

  </concept>

  <concept id="rlike">

    <title>RLIKE Operator</title>

    <conbody>

      <p>
        <indexterm audience="hidden">RLIKE operator</indexterm>
        Synonym for the <codeph>REGEXP</codeph> operator. See <xref href="impala_operators.xml#regexp"/> for details.
      </p>

      <p conref="../shared/impala_common.xml#common/example_blurb"/>

      <p>
        The following examples demonstrate the identical syntax for the <codeph>REGEXP</codeph> and <codeph>RLIKE</codeph> operators.
      </p>

<!-- Same examples shown for both REGEXP and RLIKE operators. -->

<codeblock conref="../shared/impala_common.xml#common/regexp_rlike_examples"/>

    </conbody>

  </concept>

</concept>