How Does PostgreSQL Handle NULL Value Sorting in Ascending and Descending Orders?

Null Value Sorting in PostgreSQL

Postgres handles sorting of NULL values differently depending on the sort order. By default, NULL values are sorted to the end of the table in ascending order. However, sorting in descending order behaves differently.

Descending Order Sorting

In descending order, NULL values are sorted to the top of the table by default. To override this behavior and sort NULL values to the end, PostgreSQL introduced the NULLS LAST keyword in version 8.3:

ORDER BY somevalue DESC NULLS LAST

Pre-PostgreSQL 8.3 and Non-Standard SQL Databases

For PostgreSQL versions 8.2 and earlier, or other RDBMS without the NULLS LAST feature, there is a workaround:

ORDER BY (somevalue IS NULL), somevalue DESC

This sorts NULL values last because FALSE (representing NULL) sorts before TRUE.

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