Why it matters

Window functions are essential for analytics. Understanding enables sophisticated queries.

Advertisement

The architecture

OVER clause: PARTITION BY + ORDER BY + frame.

Frame: rows between (ROWS/RANGE).

Window function structurePARTITION BYgroupsORDER BYsequence in groupFramewhich rows to includeRank, aggregates, LAG/LEAD, first/last value are common uses
Window function anatomy.
Advertisement

How it works end to end

Rank functions: RANK, DENSE_RANK, ROW_NUMBER, NTILE.

Aggregates: SUM/AVG/COUNT OVER.

Value functions: LAG, LEAD, FIRST_VALUE, LAST_VALUE.

Frame examples: 'ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW' for running totals.