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 │
└─────────┘