en draft (EXISTS)

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   │
+└──────────┘
+```

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.
 

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