!= ANY(array) does not behave as expected

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<https://stackoverflow.com/questions/23523147/sqlalchemy-and-empty-in-clause/45345041#45345041>. 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<https://www.postgresql.org/docs/current/functions-subquery.html#FUNCTIONS-SUBQUERY-NOTIN>:

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.