KITFORMA · EDITORIAL ANSWER
Why does LAST_VALUE return the current row instead of the last row in the group?
KitForma editorial guide. Window functions operate within a window frame, not necessarily the entire partition. The default frame with ordering often ends at the current peer group.
Step-by-step answer
Window functions operate within a window frame, not necessarily the entire partition. The default frame with ordering often ends at the current peer group.
For the partition’s final value, specify
ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING and a deterministic ORDER BY. Test at least three rows plus tied ordering values. Do not change the frame blindly for running totals: their intended frame is different. Confirm whether nulls should count, because PostgreSQL window behavior does not automatically implement every other database’s IGNORE NULLS option.Sources and verification
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