[SPARK-33186] Respect ANSI standard and change FIRST_VALUE as pure window function.

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Later
• Affects Version/s: 3.1.0
• Component/s: SQL
• Assignee: Unassigned
• Reporter: jiaan.geng
• Created: 20/Oct/20 03:46
• Updated: 13/Nov/20 06:22
• Resolved: 13/Nov/20 06:22

Description

FIRST_VALUE is an ANSI window function.
But the current implement of FIRST_VALUE in Spark is an aggregate function.
Although FIRST_VALUE could be used as window function.
But it is an aggregate function in fact and will lead to users to mistakenly think that FIRST_VALUE is an aggregate function that can be used.
Users can use FIRST now.