Dear Postgres users,
I like using ANY(array) instead of IN (…), as we can pass the array as binary data, avoiding the need to render its contents (which might be integers) into a SQL string, for Postgres to parse them back into integers again, and it also works with an empty list. For example:
create table foo (id integer);
insert into foo (id) values (1), (2), (3);
select * from foo where id IN (1, 2); /* returns rows 1 and 2 */
select * from foo where id = ANY (ARRAY[1, 2]); /* returns rows 1 and 2 */
However, if we try to invert it by using the != operator, then we get unexpected results:
select * from foo where id NOT IN (1, 2); /* returns row 3 only, as expected */
select * from foo where id != ANY (ARRAY[1, 2]); /* returns all rows, unexpected */
I don’t really understand why this is the case. I guess that perhaps an ANY-object has an equality operator that tests for membership of the array, but its inequality operator does something different. I don’t understand what it’s doing at all, or how it might be useful. Could anyone enlighten me?
I did find a workaround that may be useful to others (perhaps something to add to the documentation?):
select * from foo where NOT(id = ANY (ARRAY[1, 2])); /* returns row 3 only, as expected */
In a search for a solution or workaround, to pass arrays of IDs to exclude into queries, I noted that the manual says:
expression NOT IN (subquery)
The right-hand side is a parenthesized subquery, which must return exactly one column.
I tried to pass an expression that returns one column, but that failed:
select * from foo where id NOT IN (unnest(ARRAY[1, 2])); /* fails with “set-returning functions are not allowed in WHERE” */
But if I use a real subquery then it succeeds:
select * from foo where id NOT IN (SELECT * FROM unnest(ARRAY[1, 2])) /* returns row 3 only */
If the current behaviour of != ANY (ARRAY…) is not useful, then is there any support for (or opposition to) fixing it? And is it a bug that one can’t use unnest in a NOT IN expression in the WHERE clause?
Thanks, Chris.
