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Asked: 2026-06-13T05:56:12+00:00

i have severals tables, named like these: table_2012_12 table_2012_10 table_2012_07 both with the same

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i have severals tables, named like these:

table_2012_12
table_2012_10
table_2012_07

both with the same structure:

id
order_id
account_id

i know i have to perform these queries:

SELECT * FROM table_2012_12 where id=1
SELECT * FROM table_2012_12 where id=5  
SELECT * FROM table_2012_10 where id=1
SELECT * FROM table_2012_07 where id=22

What’s the best (in performances) method to use a single query?

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1 Answer

  1. Editorial Team

    The UNION operator does that. See: http://dev.mysql.com/doc/refman/5.6/en/union.html

    SELECT * FROM table_2012_12 where id=1
UNION ALL
SELECT * FROM table_2012_12 where id=5  
UNION ALL
SELECT * FROM table_2012_10 where id=1
UNION ALL
SELECT * FROM table_2012_07 where id=22

    Usually, you should not just write UNION but UNION ALL. UNION has the effect of joining the query results, as well as filtering out any duplicate rows. UNION ALL will simply merge the query results, and keep all rows. This is much more efficient

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