EXISTS | ClickHouse Docs

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.

Syntax

EXISTS(subquery)

Example

Query checking existence of values in a subquery:

Querysql

SELECT EXISTS(SELECT * FROM numbers(10) WHERE number > 8), EXISTS(SELECT * FROM numbers(10) WHERE number > 11)

Responsetext

┌─in(1, _subquery1)─┬─in(1, _subquery2)─┐
│                 1 │                 0 │
└───────────────────┴───────────────────┘

Query with a subquery returning several rows:

Querysql

SELECT count() FROM numbers(10) WHERE EXISTS(SELECT number FROM numbers(10) WHERE number > 8);

Responsetext

┌─count()─┐
│      10 │
└─────────┘

Query with a subquery that returns an empty result:

Querysql

SELECT count() FROM numbers(10) WHERE EXISTS(SELECT number FROM numbers(10) WHERE number > 11);

Responsetext

┌─count()─┐
│       0 │
└─────────┘