COALESCE

Coalesce returns the first none null argument from a set of arguments. Only the first non null argument is return, all subsequent arguments are ignored. The function will evaluate to null if all arguments are null.

Single non null argument

PGSQL> SELECT COALESCE(NULL, NULL, 'HELLO WORLD');

coalesce
--------
'HELLO WORLD'

Multiple non null arguments

PGSQL> SELECT COALESCE(NULL, NULL, 'first non null', null, null, 'second non null');

coalesce
--------
'first non null'

All null arguments

PGSQL> SELECT COALESCE(NULL, NULL, NULL);

coalesce
--------