PG Doc comments form <nore...@postgresql.org> writes: > I can't find anywhere the documentation of the SQL DATE() function which > extracts the date part out of a timestamp.
It's a type cast written in function-like syntax, as documented in https://www.postgresql.org/docs/current/sql-expressions.html#SQL-SYNTAX-TYPE-CASTS We don't really encourage that notation, because it's confusing and it doesn't work for every possible type name, which is why you won't find it mentioned very many places. > Please note that according to my tests, one can't use the cast operator when > defining expression-based indexes, while the date(column) expression is > accepted. You can if you put parentheses around it: regression=# create table t1 (f1 timestamp); CREATE TABLE regression=# create index on t1 (f1::date); ERROR: syntax error at or near "::" LINE 1: create index on t1 (f1::date); ^ regression=# create index on t1 ((f1::date)); CREATE INDEX This is per the restriction explained in the CREATE INDEX docs, that any expression-to-be-indexed that doesn't look like a function call requires parentheses. https://www.postgresql.org/docs/current/indexes-expressional.html https://www.postgresql.org/docs/current/sql-createindex.html regards, tom lane
