UNION
On this page
Combines results from multiple SELECT statements.
UNION DISTINCT
removes duplicate rows, while UNION ALL
does not remove them.UNION
is equivalent to UNION DISTINCT
.
Syntax
SELECT ...
UNION [ALL | DISTINCT] SELECT ...
[UNION [ALL | DISTINCT] SELECT ...]
Remarks
-
The first and all subsequent
SELECT
statements must select the same number of columns. -
UNION
statements are converted into nested sub-select queries by the query processor. -
The maximum depth of nested sub-select queries is 40.
Beyond this the UNION
statements are converted toTABLE
, allowing you to write up to 337 statements (0-336).
Examples
SELECT * FROM table_a UNION ALL SELECT * FROM table_b;SELECT * FROM table_a UNION SELECT * FROM table_b;
SELECT * FROM id_t UNION ALL SELECT * FROM id_t2;
+------+----------------------------------------------------------------------------+
| a | b |
+------+----------------------------------------------------------------------------+
| 1 | 0xE82C75FA86974BE7903270F4353D865C |
| 1 | 0x31343865306665352D666666322D346363362D383634622D313838303637313135653236 |
+------+----------------------------------------------------------------------------+
Last modified: March 31, 2025