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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="min"> |
| |
| <title>MIN Function</title> |
| <titlealts audience="PDF"><navtitle>MIN</navtitle></titlealts> |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="SQL"/> |
| <data name="Category" value="Impala Functions"/> |
| <data name="Category" value="Analytic Functions"/> |
| <data name="Category" value="Aggregate Functions"/> |
| <data name="Category" value="Querying"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| <indexterm audience="hidden">min() function</indexterm> |
| An aggregate function that returns the minimum value from a set of numbers. Opposite of the |
| <codeph>MAX</codeph> function. Its single argument can be numeric column, or the numeric result of a function |
| or expression applied to the column value. Rows with a <codeph>NULL</codeph> value for the specified column |
| are ignored. If the table is empty, or all the values supplied to <codeph>MIN</codeph> are |
| <codeph>NULL</codeph>, <codeph>MIN</codeph> returns <codeph>NULL</codeph>. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/syntax_blurb"/> |
| |
| <codeblock>MIN([DISTINCT | ALL] <varname>expression</varname>) [OVER (<varname>analytic_clause</varname>)]</codeblock> |
| |
| <p> |
| When the query contains a <codeph>GROUP BY</codeph> clause, returns one value for each combination of |
| grouping values. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/restrictions_sliding_window"/> |
| |
| <p conref="../shared/impala_common.xml#common/return_type_same_except_string"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p conref="../shared/impala_common.xml#common/partition_key_optimization"/> |
| |
| <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/example_blurb"/> |
| |
| <codeblock>-- Find the smallest value for this column in the table. |
| select min(c1) from t1; |
| -- Find the smallest value for this column from a subset of the table. |
| select min(c1) from t1 where month = 'January' and year = '2013'; |
| -- Find the smallest value from a set of numeric function results. |
| select min(length(s)) from t1; |
| -- Can also be used in combination with DISTINCT and/or GROUP BY. |
| -- Return more than one result. |
| select month, year, min(purchase_price) from store_stats group by month, year; |
| -- Filter the input to eliminate duplicates before performing the calculation. |
| select min(distinct x) from t1; |
| </codeblock> |
| |
| <p rev="2.0.0"> |
| The following examples show how to use <codeph>MIN()</codeph> in an analytic context. They use a table |
| containing integers from 1 to 10. Notice how the <codeph>MIN()</codeph> is reported for each input value, as |
| opposed to the <codeph>GROUP BY</codeph> clause which condenses the result set. |
| <codeblock>select x, property, min(x) over (partition by property) as min from int_t where property in ('odd','even'); |
| +----+----------+-----+ |
| | x | property | min | |
| +----+----------+-----+ |
| | 2 | even | 2 | |
| | 4 | even | 2 | |
| | 6 | even | 2 | |
| | 8 | even | 2 | |
| | 10 | even | 2 | |
| | 1 | odd | 1 | |
| | 3 | odd | 1 | |
| | 5 | odd | 1 | |
| | 7 | odd | 1 | |
| | 9 | odd | 1 | |
| +----+----------+-----+ |
| </codeblock> |
| |
| Adding an <codeph>ORDER BY</codeph> clause lets you experiment with results that are cumulative or apply to a moving |
| set of rows (the <q>window</q>). The following examples use <codeph>MIN()</codeph> in an analytic context |
| (that is, with an <codeph>OVER()</codeph> clause) to display the smallest value of <codeph>X</codeph> |
| encountered up to each row in the result set. The examples use two columns in the <codeph>ORDER BY</codeph> |
| clause to produce a sequence of values that rises and falls, to illustrate how the <codeph>MIN()</codeph> |
| result only decreases or stays the same throughout each partition within the result set. |
| The basic <codeph>ORDER BY x</codeph> clause implicitly |
| activates a window clause of <codeph>RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW</codeph>, |
| which is effectively the same as <codeph>ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW</codeph>, |
| therefore all of these examples produce the same results: |
| |
| <codeblock>select x, property, min(x) <b>over (order by property, x desc)</b> as 'minimum to this point' |
| from int_t where property in ('prime','square'); |
| +---+----------+-----------------------+ |
| | x | property | minimum to this point | |
| +---+----------+-----------------------+ |
| | 7 | prime | 7 | |
| | 5 | prime | 5 | |
| | 3 | prime | 3 | |
| | 2 | prime | 2 | |
| | 9 | square | 2 | |
| | 4 | square | 2 | |
| | 1 | square | 1 | |
| +---+----------+-----------------------+ |
| |
| select x, property, |
| min(x) over |
| ( |
| <b>order by property, x desc</b> |
| <b>range between unbounded preceding and current row</b> |
| ) as 'minimum to this point' |
| from int_t where property in ('prime','square'); |
| +---+----------+-----------------------+ |
| | x | property | minimum to this point | |
| +---+----------+-----------------------+ |
| | 7 | prime | 7 | |
| | 5 | prime | 5 | |
| | 3 | prime | 3 | |
| | 2 | prime | 2 | |
| | 9 | square | 2 | |
| | 4 | square | 2 | |
| | 1 | square | 1 | |
| +---+----------+-----------------------+ |
| |
| select x, property, |
| min(x) over |
| ( |
| <b>order by property, x desc</b> |
| <b>rows between unbounded preceding and current row</b> |
| ) as 'minimum to this point' |
| from int_t where property in ('prime','square'); |
| +---+----------+-----------------------+ |
| | x | property | minimum to this point | |
| +---+----------+-----------------------+ |
| | 7 | prime | 7 | |
| | 5 | prime | 5 | |
| | 3 | prime | 3 | |
| | 2 | prime | 2 | |
| | 9 | square | 2 | |
| | 4 | square | 2 | |
| | 1 | square | 1 | |
| +---+----------+-----------------------+ |
| </codeblock> |
| |
| The following examples show how to construct a moving window, with a running minimum taking into account all rows before |
| and 1 row after the current row. |
| Because of a restriction in the Impala <codeph>RANGE</codeph> syntax, this type of |
| moving window is possible with the <codeph>ROWS BETWEEN</codeph> clause but not the <codeph>RANGE BETWEEN</codeph> clause. |
| Because of an extra Impala restriction on the <codeph>MAX()</codeph> and <codeph>MIN()</codeph> functions in an |
| analytic context, the lower bound must be <codeph>UNBOUNDED PRECEDING</codeph>. |
| <codeblock>select x, property, |
| min(x) over |
| ( |
| <b>order by property, x desc</b> |
| <b>rows between unbounded preceding and 1 following</b> |
| ) as 'local minimum' |
| from int_t where property in ('prime','square'); |
| +---+----------+---------------+ |
| | x | property | local minimum | |
| +---+----------+---------------+ |
| | 7 | prime | 5 | |
| | 5 | prime | 3 | |
| | 3 | prime | 2 | |
| | 2 | prime | 2 | |
| | 9 | square | 2 | |
| | 4 | square | 1 | |
| | 1 | square | 1 | |
| +---+----------+---------------+ |
| |
| -- Doesn't work because of syntax restriction on RANGE clause. |
| select x, property, |
| min(x) over |
| ( |
| <b>order by property, x desc</b> |
| <b>range between unbounded preceding and 1 following</b> |
| ) as 'local minimum' |
| from int_t where property in ('prime','square'); |
| ERROR: AnalysisException: RANGE is only supported with both the lower and upper bounds UNBOUNDED or one UNBOUNDED and the other CURRENT ROW. |
| </codeblock> |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/related_info"/> |
| |
| <p> |
| <xref href="impala_analytic_functions.xml#analytic_functions"/>, <xref href="impala_max.xml#max"/>, |
| <xref href="impala_avg.xml#avg"/> |
| </p> |
| </conbody> |
| </concept> |