mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-14 18:32:29 +00:00
959 B
959 B
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 be used in a WHERE clause.
:::tip
References to main query tables and columns are not supported in a subquery.
:::
Syntax
WHERE EXISTS(subquery)
Example
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 │
└─────────┘