ClickHouse/docs/en/sql-reference/operators/exists.md

EXISTS

The EXISTS operator tests how many records are in the result of a subquery. If it is empty, then the operator returns 0. Otherwise it returns 1.

!!! warning "Warning" References to main query tables and columns are not supported in a subquery.

Syntax

WHERE EXISTS(subquery)

Example

Query:

SELECT 'Exists' WHERE EXISTS (SELECT * FROM numbers(10) WHERE number < 2);
SELECT 'Empty subquery' WHERE EXISTS (SELECT * FROM numbers(10) WHERE number > 12);

The first query returns one row. The second query does not return rows because the result of the subquery is empty.

┌─'Exists'─┐
│ Exists   │
└──────────┘