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UNION

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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.

    Note

    The maximum allowed depth of nested sub-select queries is 40.

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: April 3, 2024

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