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first aggregate function

  • Άρθρο

Applies to: check marked yes Databricks SQL check marked yes Databricks Runtime

Returns the first value of expr for a group of rows. This function is a synonym for first_value aggregate function.

Syntax

first(expr[, ignoreNull]) [FILTER ( WHERE cond ) ]

This function can also be invoked as a window function using the OVER clause.

Arguments

  • expr: An expression of any type.
  • ignoreNull: An optional BOOLEAN literal that defaults to false.
  • cond: An optional boolean expression filtering the rows used for aggregation.
  • IGNORE NULLS or RESPECT NULLS: When IGNORE NULLS is used or ignoreNull is true any expr value that is NULL is ignored. The default is RESPECT NULLS.

Returns

The result has the same type as expr.

This function is non-deterministic.

Examples

> SELECT first(col) FROM VALUES (10), (5), (20) AS tab(col);
 10

> SELECT first(col) FROM VALUES (NULL), (5), (20) AS tab(col);
 NULL

> SELECT first(col, true) FROM VALUES (NULL), (5), (20) AS tab(col);
 5

> SELECT first(col) IGNORE NULLS FROM VALUES (10), (5), (NULL) AS tab(col);
 5

> SELECT first(col) FILTER (WHERE col > 5) FROM VALUES (5), (20) AS tab(col);
 20