Learning PostgreSQL by 2015

Author:2015
Language: eng
Format: epub, mobi
Publisher: Packt Publishing

The ending point—frame_end—can be any one of the following:

<value> PRECEDING

CURRENT ROW

<value> FOLLOWING

UNBOUNDED PRECEDING—the very last record of the partition.

The starting point should precede the ending point. That's why, for example, ROWS BETWEEN CURRENT ROW AND 1 PRECEDING is not correct.

A window frame can be defined using the ROWS mode or the RANGE mode. It affects the meaning of the CURRENT ROW. In the ROWS mode, the CURRENT ROW points to the current record itself. In the RANGE mode, the CURRENT ROW points to the first or to the last record that has the same position when sorted according to the ORDER BY clause. First or last will be chosen with a view to make the frame wider.

If frame_end is omitted, then CURRENT ROW is used instead.

If the whole frame clause is omitted, then the frame will be built using the RANGE UNBOUNDED PRECEDING definition.

Look at the following example of a window definition:

OVER (PARTITION BY a ORDER BY b ROWS BETWEEN UNBOUNDED PRECEDING AND 5 FOLLOWING)

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