From 398e164e46df4b0a79ec62c4e9445b646c22f95a Mon Sep 17 00:00:00 2001
From: Alexey <lehasm@gmail.com>
Date: Fri, 12 Nov 2021 20:02:26 +0000
Subject: [PATCH] en draft (EXISTS)

---
 docs/en/sql-reference/operators/exists.md     | 29 +++++++++++++++++++
 docs/en/sql-reference/operators/index.md      |  2 +-
 .../sql-reference/statements/select/where.md  |  4 +++
 3 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 docs/en/sql-reference/operators/exists.md

diff --git a/docs/en/sql-reference/operators/exists.md b/docs/en/sql-reference/operators/exists.md
new file mode 100644
index 00000000000..929da871655
--- /dev/null
+++ b/docs/en/sql-reference/operators/exists.md
@@ -0,0 +1,29 @@
+# EXISTS {#exists-operator}
+
+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**
+
+```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. The second query does not return rows because the result of the subquery is empty.
+
+``` text
+┌─'Exists'─┐
+│ Exists   │
+└──────────┘
+```
diff --git a/docs/en/sql-reference/operators/index.md b/docs/en/sql-reference/operators/index.md
index efbc600fdd4..1c59b25fc63 100644
--- a/docs/en/sql-reference/operators/index.md
+++ b/docs/en/sql-reference/operators/index.md
@@ -71,7 +71,7 @@ For tuple subtraction: [tupleMinus](../../sql-reference/functions/tuple-function
 
 ## Operators for Working with Data Sets {#operators-for-working-with-data-sets}
 
-*See [IN operators](../../sql-reference/operators/in.md).*
+See [IN operators](../../sql-reference/operators/in.md) and [EXISTS](../../sql-reference/operators/exists.md) operator.
 
 `a IN ...` – The `in(a, b)` function.
 
diff --git a/docs/en/sql-reference/statements/select/where.md b/docs/en/sql-reference/statements/select/where.md
index 69505a51db4..ffc9a38b5fb 100644
--- a/docs/en/sql-reference/statements/select/where.md
+++ b/docs/en/sql-reference/statements/select/where.md
@@ -12,3 +12,7 @@ If there is a `WHERE` clause, it must contain an expression with the `UInt8` typ
 
 !!! note "Note"
     There’s a filtering optimization called [prewhere](../../../sql-reference/statements/select/prewhere.md).
+
+**See Also**
+
+-   [EXISTS](../../../sql-reference/operators/exists.md) operator