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Overview A window function applies an aggregation to some subset of the rows selected by a query. The selected rows are preserved in the query output, rather than being grouped into a single output row as they would be in a non-window aggregation.
For details on how window functions work, see the Postgres documentation for Window Function .
Syntax
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function_name ([ expression [, expression ...]]) OVER (
[ PARTITION BY expression [, ...] ]
[ ORDER BY expression [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] ]
[ frame_clause ]
) The optional frame_clause has the following syntax:
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{ RANGE | ROWS } frame_start
| { RANGE | ROWS } BETWEEN frame_start AND frame_end The frame_start and frame_end expressions can be one of the following:
UNBOUNDED PRECEDINGoffset PRECEDINGCURRENT ROWoffset FOLLOWINGUNBOUNDED FOLLOWINGFunctions The functions below can be used in windows, along with the aggregation functions .
row_number Name Return type Description row_number() integer Returns the number of the current row within its partition, counting from 1.
rank Name Return type Description rank() integer Returns the rank of the current row, with gaps (the row_number of the first row in its peer group).
dense_rank Name Return type Description dense_rank() integer Returns the rank of the current row, without gaps. This function effectively counts peer groups.
first_value Name Return type Description first_value(value T ) T Returns the value evaluated at the row that is the first row of the window frame.
last_value Name Return type Description last_value(value T ) T Returns the value evaluated at the row that is the last row of the window frame.
