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In the following example, t3 has a column named c instead of b. But everything seems to work, even when a SELECT explicitly names b:
MariaDB [test]> CREATE TABLE t1 (
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-> a INT,
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-> b INT
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-> ) ENGINE = MyISAM;
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Query OK, 0 rows affected (0.07 sec)
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MariaDB [test]> CREATE TABLE t2 (
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-> a INT,
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-> b INT
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-> ) ENGINE = MyISAM;
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Query OK, 0 rows affected (0.06 sec)
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MariaDB [test]> CREATE TABLE t3 (
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-> a INT,
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-> c INT
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-> ) ENGINE = MyISAM;
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Query OK, 0 rows affected (0.02 sec)
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MariaDB [test]> CREATE TABLE t_mrg (
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-> a INT,
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-> b INT
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-> ) ENGINE = MERGE,UNION=(t1,t2,t3);
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Query OK, 0 rows affected (0.02 sec)
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MariaDB [test]> INSERT INTO t1 VALUES (1,1);
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Query OK, 1 row affected (0.02 sec)
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MariaDB [test]> INSERT INTO t3 VALUES (2,2);
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Query OK, 1 row affected (0.00 sec)
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MariaDB [test]> SELECT a,b FROM t_mrg;
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+------+------+
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| a | b |
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+------+------+
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| 1 | 1 |
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| 2 | 2 |
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+------+------+
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2 rows in set (0.00 sec)
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From MySQL manual:
http://dev.mysql.com/doc/refman/5.5/en/merge-storage-engine.html
The MERGE storage engine, also known as the MRG_MyISAM engine, is a collection of identical MyISAM tables that can be used as one. “Identical” means that all tables have identical column and index information.
As far as I understand, this includes column names?
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