[SPARK-28648] Adds support to `groups` unit type in window clauses

• Type: Sub-task
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.0.0
• Component/s: SQL
• Assignee: Unassigned
• Reporter: Dylan Guedes
• Created: 07/Aug/19 18:27
• Updated: 25/Nov/20 10:07

Description

Spark currently support the two most common window functions unit types: rows and ranges. However, in PgSQL a new type was added: `groups`. 

According to this source, the difference is:
"""ROWS counts the exact number of rows in the frame.
RANGE performs logical windowing where we don’t count the number of rows, but look for a value offset.
GROUPS counts all groups of tied rows within the window."""