mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-25 09:02:00 +00:00
b75653e449
The existing documentation for EXISTS makes it look like it only works as part of a WHERE clause, when in fact, it can be used in many places. Changing the docs to note that a bit differently with another example should provide more clarity on the use of this term.
63 lines
1.4 KiB
Markdown
63 lines
1.4 KiB
Markdown
---
|
|
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 also be used in a [WHERE](../../sql-reference/statements/select/where.md) clause.
|
|
|
|
:::tip
|
|
References to main query tables and columns are not supported in a subquery.
|
|
:::
|
|
|
|
**Syntax**
|
|
|
|
``` sql
|
|
EXISTS(subquery)
|
|
```
|
|
|
|
**Example**
|
|
|
|
Query checking existence of values in a subquery:
|
|
|
|
``` sql
|
|
SELECT EXISTS(SELECT * FROM numbers(10) WHERE number > 8), EXISTS(SELECT * FROM numbers(10) WHERE number > 11)
|
|
```
|
|
|
|
Result:
|
|
|
|
``` text
|
|
┌─in(1, _subquery1)─┬─in(1, _subquery2)─┐
|
|
│ 1 │ 0 │
|
|
└───────────────────┴───────────────────┘
|
|
```
|
|
|
|
Query with a subquery returning several rows:
|
|
|
|
``` sql
|
|
SELECT count() FROM numbers(10) WHERE EXISTS(SELECT number FROM numbers(10) WHERE number > 8);
|
|
```
|
|
|
|
Result:
|
|
|
|
``` text
|
|
┌─count()─┐
|
|
│ 10 │
|
|
└─────────┘
|
|
```
|
|
|
|
Query with a subquery that returns an empty result:
|
|
|
|
``` sql
|
|
SELECT count() FROM numbers(10) WHERE EXISTS(SELECT number FROM numbers(10) WHERE number > 11);
|
|
```
|
|
|
|
Result:
|
|
|
|
``` text
|
|
┌─count()─┐
|
|
│ 0 │
|
|
└─────────┘
|
|
```
|