mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-09-20 08:40:50 +00:00
b75653e449
The existing documentation for EXISTS makes it look like it only works as part of a WHERE clause, when in fact, it can be used in many places. Changing the docs to note that a bit differently with another example should provide more clarity on the use of this term.
1.4 KiB
1.4 KiB
| slug |
|---|
| /en/sql-reference/operators/exists |
EXISTS
The EXISTS operator checks how many records are in the result of a subquery. If it is empty, then the operator returns 0. Otherwise, it returns 1.
EXISTS can also be used in a WHERE clause.
:::tip
References to main query tables and columns are not supported in a subquery.
:::
Syntax
EXISTS(subquery)
Example
Query checking existence of values in a subquery:
SELECT EXISTS(SELECT * FROM numbers(10) WHERE number > 8), EXISTS(SELECT * FROM numbers(10) WHERE number > 11)
Result:
┌─in(1, _subquery1)─┬─in(1, _subquery2)─┐
│ 1 │ 0 │
└───────────────────┴───────────────────┘
Query with a subquery returning several rows:
SELECT count() FROM numbers(10) WHERE EXISTS(SELECT number FROM numbers(10) WHERE number > 8);
Result:
┌─count()─┐
│ 10 │
└─────────┘
Query with a subquery that returns an empty result:
SELECT count() FROM numbers(10) WHERE EXISTS(SELECT number FROM numbers(10) WHERE number > 11);
Result:
┌─count()─┐
│ 0 │
└─────────┘