Combines results from multiple SELECT statements. UNION removes duplicate rows, while UNION ALL leaves them. UNION DISTINCT has the same semantics as the default UNION.

SELECT ...
UNION [ALL | DISTINCT] SELECT ...
[UNION [ALL | DISTINCT] SELECT ...]

Notes

• UNION ALL does not remove duplicate rows from the result set.
• The first and all subsequent SELECT statements must select the same number of columns.
• MemSQL does not support ORDER BY or GROUP BY on the result of a UNION. For example, the query (SELECT * FROM table_a UNION ALL SELECT * FROM table_b) GROUP BY x is not supported.

Example

memsql> SELECT * FROM table_a UNION ALL SELECT * FROM table_b;
memsql> SELECT * FROM table_a UNION SELECT * FROM table_b;

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