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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="conditional_functions"> |
| |
| <title>Impala Conditional Functions</title> |
| |
| <titlealts audience="PDF"> |
| |
| <navtitle>Conditional Functions</navtitle> |
| |
| </titlealts> |
| |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Functions"/> |
| <data name="Category" value="SQL"/> |
| <data name="Category" value="Data Analysts"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Querying"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| Impala supports the following conditional functions for testing equality, comparison |
| operators, and nullity: |
| </p> |
| |
| <ul> |
| <li> |
| <xref href="#conditional_functions/case">CASE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/case2">CASE2</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/coalesce">COALESCE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/decode">DECODE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/if">IF</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/ifnull">IFNULL</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/isfalse">ISFALSE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/isnotfalse">ISNOTFALSE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/isnottrue">ISNOTTRUE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/isnull">ISNULL</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/istrue">ISTRUE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/nonnullvalue">NONNULLVALUE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/nullif">NULLIF</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/nullifzero">NULLIFZERO</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/nullvalue">NULLVALUE</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/nvl">NVL</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/nvl2">NVL2</xref> |
| </li> |
| |
| <li> |
| <xref href="#conditional_functions/zeroifnull">ZEROIFNULL</xref> |
| </li> |
| </ul> |
| |
| <dl> |
| <dlentry id="case"> |
| |
| <dt> |
| CASE a WHEN b THEN c [WHEN d THEN e]... [ELSE f] END |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Compares an expression to one or more possible values, and returns a |
| corresponding result when a match is found. |
| <p |
| conref="../shared/impala_common.xml#common/return_same_type"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p> |
| In this form of the <codeph>CASE</codeph> expression, the initial value |
| <codeph>A</codeph> being evaluated for each row it typically a column reference, or |
| an expression involving a column. This form can only compare against a set of |
| specified values, not ranges, multi-value comparisons such as |
| <codeph>BETWEEN</codeph> or <codeph>IN</codeph>, regular expressions, or |
| <codeph>NULL</codeph>. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/example_blurb"/> |
| |
| <p> |
| Although this example is split across multiple lines, you can put any or all parts |
| of a <codeph>CASE</codeph> expression on a single line, with no punctuation or other |
| separators between the <codeph>WHEN</codeph>, <codeph>ELSE</codeph>, and |
| <codeph>END</codeph> clauses. |
| </p> |
| <codeblock>select case x |
| when 1 then 'one' |
| when 2 then 'two' |
| when 0 then 'zero' |
| else 'out of range' |
| end |
| from t1; |
| </codeblock> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="case2"> |
| |
| <dt> |
| CASE WHEN a THEN b [WHEN c THEN d]... [ELSE e] END |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Tests whether any of a sequence of expressions is |
| <codeph>TRUE</codeph>, and returns a corresponding result for the first true |
| expression. |
| <p |
| conref="../shared/impala_common.xml#common/return_same_type"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p> |
| <codeph>CASE</codeph> expressions without an initial test value have more |
| flexibility. For example, they can test different columns in different |
| <codeph>WHEN</codeph> clauses, or use comparison operators such as |
| <codeph>BETWEEN</codeph>, <codeph>IN</codeph> and <codeph>IS NULL</codeph> rather |
| than comparing against discrete values. |
| </p> |
| |
| <p> |
| <codeph>CASE</codeph> expressions are often the foundation of long queries that |
| summarize and format results for easy-to-read reports. For example, you might use a |
| <codeph>CASE</codeph> function call to turn values from a numeric column into |
| category strings corresponding to integer values, or labels such as <q>Small</q>, |
| <q>Medium</q> and <q>Large</q> based on ranges. Then subsequent parts of the query |
| might aggregate based on the transformed values, such as how many values are |
| classified as small, medium, or large. You can also use <codeph>CASE</codeph> to |
| signal problems with out-of-bounds values, <codeph>NULL</codeph> values, and so on. |
| </p> |
| |
| <p> |
| By using operators such as <codeph>OR</codeph>, <codeph>IN</codeph>, |
| <codeph>REGEXP</codeph>, and so on in <codeph>CASE</codeph> expressions, you can |
| build extensive tests and transformations into a single query. Therefore, |
| applications that construct SQL statements often rely heavily on |
| <codeph>CASE</codeph> calls in the generated SQL code. |
| </p> |
| |
| <p> |
| Because this flexible form of the <codeph>CASE</codeph> expressions allows you to |
| perform many comparisons and call multiple functions when evaluating each row, be |
| careful applying elaborate <codeph>CASE</codeph> expressions to queries that process |
| large amounts of data. For example, when practical, evaluate and transform values |
| through <codeph>CASE</codeph> after applying operations such as aggregations that |
| reduce the size of the result set; transform numbers to strings after performing |
| joins with the original numeric values. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/example_blurb"/> |
| |
| <p> |
| Although this example is split across multiple lines, you can put any or all parts |
| of a <codeph>CASE</codeph> expression on a single line, with no punctuation or other |
| separators between the <codeph>WHEN</codeph>, <codeph>ELSE</codeph>, and |
| <codeph>END</codeph> clauses. |
| </p> |
| <codeblock>select case |
| when dayname(now()) in ('Saturday','Sunday') then 'result undefined on weekends' |
| when x > y then 'x greater than y' |
| when x = y then 'x and y are equal' |
| when x is null or y is null then 'one of the columns is null' |
| else null |
| end |
| from t1; |
| </codeblock> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="coalesce"> |
| |
| <dt> |
| COALESCE(type v1, type v2, ...) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns the first specified argument that is not |
| <codeph>NULL</codeph>, or <codeph>NULL</codeph> if all arguments are |
| <codeph>NULL</codeph>. |
| <p |
| conref="../shared/impala_common.xml#common/return_same_type"/> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry rev="2.0.0" id="decode"> |
| |
| <dt> |
| DECODE(type expression, type search1, type result1 [, type search2, type result2 ...] |
| [, type default] ) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Compares the first argument, <codeph>expression</codeph>, to the |
| <codeph>search</codeph> expressions using the <codeph>IS NOT DISTINCT</codeph> |
| operator, and returns: |
| <ul> |
| <li> |
| The corresponding <codeph>result</codeph> when a match is found. |
| </li> |
| |
| <li> |
| The first corresponding <codeph>result</codeph> if there are more than one |
| matching <codeph>search</codeph> expressions. |
| </li> |
| |
| <li> |
| The <codeph>default</codeph> expression if none of the search expressions matches |
| the first argument <codeph>expression</codeph>. |
| </li> |
| |
| <li> |
| <codeph>NULL</codeph> if the final <codeph>default</codeph> expression is omitted |
| and none of the <codeph>search</codeph> expressions matches the first argument. |
| </li> |
| </ul> |
| <p> |
| <b>Return type:</b> Same as the first argument with the following exceptions: |
| <ul> |
| <li> |
| Integer values are promoted to <codeph>BIGINT</codeph>. |
| </li> |
| |
| <li> |
| Floating-point values are promoted to <codeph>DOUBLE</codeph>. |
| </li> |
| |
| <li> |
| Use <codeph>CAST()</codeph> when inserting into a smaller numeric column. |
| </li> |
| </ul> |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| <ul> |
| <li> |
| Can be used as shorthand for a <codeph>CASE</codeph> expression. |
| </li> |
| |
| <li> |
| The first argument, <codeph>expression</codeph>, and the search expressions must |
| be of the same type or convertible types. |
| </li> |
| |
| <li> |
| The result expression can be a different type, but all result expressions must be |
| of the same type. |
| </li> |
| |
| <li> |
| Returns a successful match if the first argument is <codeph>NULL</codeph> and a |
| search expression is also <codeph>NULL</codeph>. |
| </li> |
| |
| <li> |
| <codeph>NULL</codeph> can be used as a search expression. |
| </li> |
| </ul> |
| <p conref="../shared/impala_common.xml#common/example_blurb"/> |
| |
| <p> |
| The following example translates numeric day values into weekday names, such as 1 to |
| Monday, 2 to Tuesday, etc. |
| </p> |
| <codeblock>SELECT event, DECODE(day_of_week, 1, "Monday", 2, "Tuesday", 3, "Wednesday", |
| 4, "Thursday", 5, "Friday", 6, "Saturday", 7, "Sunday", "Unknown day") |
| FROM calendar; |
| </codeblock> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="if"> |
| |
| <dt> |
| IF(BOOLEAN condition, type ifTrue, type ifFalseOrNull) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Tests an expression and returns a corresponding result depending on |
| whether the result is <codeph>TRUE</codeph>, <codeph>FALSE</codeph>, or |
| <codeph>NULL</codeph>. |
| <p> |
| <b>Return type:</b> Same as the <codeph>ifTrue</codeph> argument value |
| </p> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry rev="1.3.0" id="ifnull"> |
| |
| <dt> |
| IFNULL(type a, type ifNull) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Alias for the <codeph>ISNULL()</codeph> function, with the same |
| behavior. To simplify porting SQL with vendor extensions to Impala. |
| <p conref="../shared/impala_common.xml#common/added_in_130"/> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="isfalse" rev="2.2.0"> |
| |
| <dt> |
| ISFALSE(BOOLEAN expression) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns <codeph>TRUE</codeph> if the expression is |
| <codeph>FALSE</codeph>. Returns <codeph>FALSE</codeph> if the expression is |
| <codeph>TRUE</codeph> or <codeph>NULL</codeph>. |
| <p> |
| Same as the <codeph>IS FALSE</codeph> operator. |
| </p> |
| |
| <p> |
| Similar to <codeph>ISNOTTRUE()</codeph>, except it returns the opposite value for a |
| <codeph>NULL</codeph> argument. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/return_type_boolean"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_220"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p |
| conref="../shared/impala_common.xml#common/boolean_functions_vs_expressions" |
| /> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="isnotfalse" rev="2.2.0"> |
| |
| <dt> |
| ISNOTFALSE(BOOLEAN expression) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Tests if a Boolean expression is not <codeph>FALSE</codeph> (that is, |
| either <codeph>TRUE</codeph> or <codeph>NULL</codeph>). Returns <codeph>TRUE</codeph> |
| if so. If the argument is <codeph>NULL</codeph>, returns <codeph>TRUE</codeph>. |
| <p> |
| Same as the <codeph>IS NOT FALSE</codeph> operator. |
| </p> |
| |
| <p> |
| Similar to <codeph>ISTRUE()</codeph>, except it returns the opposite value for a |
| <codeph>NULL</codeph> argument. |
| </p> |
| |
| <p |
| conref="../shared/impala_common.xml#common/return_type_boolean"/> |
| |
| <p conref="../shared/impala_common.xml#common/for_compatibility_only"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_220"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p |
| conref="../shared/impala_common.xml#common/boolean_functions_vs_expressions" |
| /> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="isnottrue" rev="2.2.0"> |
| |
| <dt> |
| ISNOTTRUE(BOOLEAN expression) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Tests if a Boolean expression is not <codeph>TRUE</codeph> (that is, |
| either <codeph>FALSE</codeph> or <codeph>NULL</codeph>). Returns <codeph>TRUE</codeph> |
| if so. If the argument is <codeph>NULL</codeph>, returns <codeph>TRUE</codeph>. |
| <p> |
| Same as the <codeph>IS NOT TRUE</codeph> operator. |
| </p> |
| |
| <p> |
| Similar to <codeph>ISFALSE()</codeph>, except it returns the opposite value for a |
| <codeph>NULL</codeph> argument. |
| </p> |
| |
| <p |
| conref="../shared/impala_common.xml#common/return_type_boolean"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_220"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p |
| conref="../shared/impala_common.xml#common/boolean_functions_vs_expressions" |
| /> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="isnull"> |
| |
| <dt> |
| ISNULL(type a, type ifNull) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Tests if an expression is <codeph>NULL</codeph>, and returns the |
| expression result value if not. If the first argument is <codeph>NULL</codeph>, |
| returns the second argument. |
| <p> |
| <b>Compatibility notes:</b> Equivalent to the <codeph>NVL()</codeph> function from |
| Oracle Database or <codeph>IFNULL()</codeph> from MySQL. The <codeph>NVL()</codeph> |
| and <codeph>IFNULL()</codeph> functions are also available in Impala. |
| </p> |
| |
| <p> |
| <b>Return type:</b> Same as the first argument value |
| </p> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="istrue" rev="2.2.0"> |
| |
| <dt> |
| ISTRUE(BOOLEAN expression) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns <codeph>TRUE</codeph> if the expression is |
| <codeph>TRUE</codeph>. Returns <codeph>FALSE</codeph> if the expression is |
| <codeph>FALSE</codeph> or <codeph>NULL</codeph>. |
| <p> |
| Same as the <codeph>IS TRUE</codeph> operator. |
| </p> |
| |
| <p> |
| Similar to <codeph>ISNOTFALSE()</codeph>, except it returns the opposite value for a |
| <codeph>NULL</codeph> argument. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/return_type_boolean"/> |
| |
| <p conref="../shared/impala_common.xml#common/for_compatibility_only"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_220"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p |
| conref="../shared/impala_common.xml#common/boolean_functions_vs_expressions" |
| /> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="nonnullvalue" rev="2.2.0"> |
| |
| <dt> |
| NONNULLVALUE(type expression) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns <codeph>TRUE</codeph> if the expression is non-null and |
| returns <codeph>FALSE</codeph> if the expression is <codeph>NULL</codeph>. |
| <p> |
| Same as the <codeph>IS NOT NULL</codeph> operator. |
| </p> |
| |
| <p> |
| The converse of <codeph>NULLVALUE()</codeph>. |
| </p> |
| |
| <p |
| conref="../shared/impala_common.xml#common/return_type_boolean"/> |
| |
| <p conref="../shared/impala_common.xml#common/for_compatibility_only"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_220"/> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry rev="1.3.0" id="nullif"> |
| |
| <dt> |
| NULLIF(type expr1, type expr2) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns <codeph>NULL</codeph> if the two specified arguments are |
| equal. If the specified arguments are not equal, returns the value of |
| <varname>expr1</varname>. The data types of the expressions must be compatible, |
| according to the conversion rules from <xref href="impala_datatypes.xml#datatypes"/>. |
| You cannot use an expression that evaluates to <codeph>NULL</codeph> for |
| <varname>expr1</varname>; that way, you can distinguish a return value of |
| <codeph>NULL</codeph> from an argument value of <codeph>NULL</codeph>, which would |
| never match <varname>expr2</varname>. |
| <p> |
| <b>Usage notes:</b> This function is effectively shorthand for a |
| <codeph>CASE</codeph> expression of the form: |
| </p> |
| <codeblock>CASE |
| WHEN <varname>expr1</varname> = <varname>expr2</varname> THEN NULL |
| ELSE <varname>expr1</varname> |
| END</codeblock> |
| <p> |
| It is commonly used in division expressions, to produce a <codeph>NULL</codeph> |
| result instead of a divide-by-zero error when the divisor is equal to zero: |
| </p> |
| <codeblock>select 1.0 / nullif(c1,0) as reciprocal from t1;</codeblock> |
| <p> |
| You might also use it for compatibility with other database systems that support the |
| same <codeph>NULLIF()</codeph> function. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/return_same_type"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_130"/> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry rev="1.3.0" id="nullifzero"> |
| |
| <dt> |
| NULLIFZERO(type numeric_expr) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns <codeph>NULL</codeph> if the numeric expression evaluates to |
| 0, otherwise returns the result of the expression. |
| <p> |
| <b>Usage notes:</b> Used to avoid error conditions such as divide-by-zero in numeric |
| calculations. Serves as shorthand for a more elaborate <codeph>CASE</codeph> |
| expression, to simplify porting SQL with vendor extensions to Impala. |
| </p> |
| |
| <p> |
| <b>Return type:</b> Same type as the input argument |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_130"/> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="nullvalue" rev="2.2.0"> |
| |
| <dt> |
| NULLVALUE(type expression) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns <codeph>TRUE</codeph> if the expression is |
| <codeph>NULL</codeph>, and returns <codeph>FALSE</codeph> otherwise. |
| <p> |
| Same as the <codeph>IS NULL</codeph> operator. |
| </p> |
| |
| <p> |
| The converse of <codeph>NONNULLVALUE()</codeph>. |
| </p> |
| |
| <p |
| conref="../shared/impala_common.xml#common/return_type_boolean"/> |
| |
| <p conref="../shared/impala_common.xml#common/for_compatibility_only"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_220"/> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="nvl" rev="1.1"> |
| |
| <dt> |
| NVL(type a, type ifNull) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Alias for the <codeph>ISNULL()</codeph> function. Returns the first |
| argument if the first argument is not <codeph>NULL</codeph>. Returns the second |
| argument if the first argument is <codeph>NULL</codeph>. |
| <p> |
| Equivalent to the <codeph>NVL()</codeph> function in Oracle Database or |
| <codeph>IFNULL()</codeph> in MySQL. |
| </p> |
| |
| <p> |
| <b>Return type:</b> Same as the first argument value |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_11"/> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry id="nvl2" rev="2.9.0 IMPALA-5030"> |
| |
| <dt> |
| NVL2(type a, type ifNotNull, type ifNull) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns the second argument, |
| <codeph>ifNotNull</codeph>, if the first argument is not |
| <codeph>NULL</codeph>. Returns the third argument, |
| <codeph>ifNull</codeph>, if the first argument is |
| <codeph>NULL</codeph>. <p> Equivalent to the <codeph>NVL2()</codeph> |
| function in Oracle Database. </p> |
| <p> |
| <b>Return type:</b> Same as the first argument value </p> |
| <p conref="../shared/impala_common.xml#common/added_in_290"/> |
| <p conref="../shared/impala_common.xml#common/example_blurb"/> |
| <codeblock> |
| SELECT NVL2(NULL, 999, 0); -- Returns 0 |
| SELECT NVL2('ABC', 'Is Not Null', 'Is Null'); -- Returns 'Is Not Null'</codeblock> |
| </dd> |
| |
| </dlentry> |
| |
| <dlentry rev="1.3.0" id="zeroifnull"> |
| |
| <dt> |
| ZEROIFNULL(type numeric_expr) |
| </dt> |
| |
| <dd> |
| <b>Purpose:</b> Returns 0 if the numeric expression evaluates to |
| <codeph>NULL</codeph>, otherwise returns the result of the expression. |
| <p> |
| <b>Usage notes:</b> Used to avoid unexpected results due to unexpected propagation |
| of <codeph>NULL</codeph> values in numeric calculations. Serves as shorthand for a |
| more elaborate <codeph>CASE</codeph> expression, to simplify porting SQL with vendor |
| extensions to Impala. |
| </p> |
| |
| <p> |
| <b>Return type:</b> Same type as the input argument |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_130"/> |
| </dd> |
| |
| </dlentry> |
| </dl> |
| |
| </conbody> |
| |
| </concept> |
