Обсуждение: != 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. 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.
Chris Wilson schrieb am 07.12.2018 um 13:39: > 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 */ id <> ANY (...) means: return "true" if at least one of the elements is not equal to the value on the left side. What you are looking for is the ALL operator select * from foo where id <> ALL (ARRAY[1, 2]); That is essentially the equivalent to NOT IN
Thomas Kellerer schrieb am 07.12.2018 um 13:48: > Chris Wilson schrieb am 07.12.2018 um 13:39: >> 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 */ > > id <> ANY (...) means: return "true" if at least one of the elements is not equal to the value on the left side. > > What you are looking for is the ALL operator > > select * > from foo > where id <> ALL (ARRAY[1, 2]); > > That is essentially the equivalent to NOT IN See here for a longer explanation: https://stackoverflow.com/a/10675636
Thomas Kellerer schrieb am 07.12.2018 um 13:48:
> Chris Wilson schrieb am 07.12.2018 um 13:39:
>> 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 */
>
> id <> ANY (...) means: return "true" if at least one of the elements is not equal to the value on the left side.
>
> What you are looking for is the ALL operator
>
> select *
> from foo
> where id <> ALL (ARRAY[1, 2]);
>
> That is essentially the equivalent to NOT IN
https://stackoverflow.com/a/10675636
Ken
![](http://agency-software.org/demo/client/images/agency_logo_small.png)
>>>>> "Chris" == Chris Wilson <chris.wilson@cantabcapital.com> writes: Chris> However, if we try to invert it by using the != operator, then Chris> we get unexpected results: Mr. De Morgan would like a word. https://en.wikipedia.org/wiki/De_Morgan%27s_laws In short, if you have a condition of the form (a OR b) and you want to negate it, then you find that: NOT (a OR b) is equivalent to (NOT a) AND (NOT b) Since x = ANY (array[1,2]) is equivalent to (x = 1) OR (x = 2), then the negation would be (x != 1) AND (x != 2), not OR. Which can be conveniently expressed as x != ALL (array[1,2]). So just as you interchange AND and OR when inverting the sense of a condition, you also interchange ALL and ANY for exactly the same reasons. Chris> expression NOT IN (subquery) https://wiki.postgresql.org/wiki/Don%27t_Do_This#Don.27t_use_NOT_IN Chris> And is it a bug that one can't use unnest in a NOT IN expression Chris> in the WHERE clause? No. -- Andrew (irc:RhodiumToad)