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

# EXISTS {#exists-operator}

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](../../sql-reference/statements/select/where.md) clause.

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

**Syntax**

```sql
WHERE EXISTS(subquery)
```

**Example**

Query:

``` sql
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 while the second query does not return rows because the result of the subquery is empty:

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