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Returns the first value evaluated in the specified window frame. If there are no rows in the window frame, returns NULL.

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Syntax

FIRST_VALUE( <expression> ) OVER ( [ PARTITION BY <partition_by> ] ORDER BY <order_by> [ASC|DESC] )

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Parameters

ParameterDescriptionSupported input types
<expression>A SQL expression of any type to evaluate.Any
<partition_by>An expression used for the PARTITION BY clause.Any
<order_by>An expression used for the order by clause.Any

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Return Types

Same as the input type of <expression>. This function respects NULL values, and the results will be ordered with the default NULL ordering NULLS LAST unless otherwise specified in the ORDER BY clause. If no ORDER BY clause is applied, the order will be undefined.

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Examples

The following code example selects the nickname, level, current_score, and highest_score for each level, using the NTH_VALUE function to retrieve the top score within each level, ordered by current_score in descending order. Example The following query uses UNNEST to convert an array [1,2,5] into a column, order the values, and returns the first value as result. It returns the first element after ordering. 
SELECT FIRST_VALUE(a) OVER (ORDER BY a) as result FROM UNNEST(array[1,2,5]) as a;
result int null
1
1
1

Rows: 3Execution time: 5ms

Example The following query uses UNNEST to convert an array [100, NULL, 1] into a column, order the values, and returns the first value as result. It returns NULL values because ORDER BY specifies ‘nulls first’. 
SELECT FIRST_VALUE(a) OVER (ORDER BY a desc nulls first) as result FROM UNNEST(array[100,NULL,1]) as a;
result int null
NULL
NULL
NULL

Rows: 3Execution time: 5ms