Details
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Type:
Bug
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Status: Closed
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Priority:
Minor
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Resolution: Not a Bug
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Affects Version/s: None
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Fix Version/s: None
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Component/s: None
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Labels:None
Description
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 (
-> a INT,
-> b INT
-> ) ENGINE = MyISAM;
Query OK, 0 rows affected (0.07 sec)
MariaDB [test]> CREATE TABLE t2 (
-> a INT,
-> b INT
-> ) ENGINE = MyISAM;
Query OK, 0 rows affected (0.06 sec)
MariaDB [test]> CREATE TABLE t3 (
-> a INT,
-> c INT
-> ) ENGINE = MyISAM;
Query OK, 0 rows affected (0.02 sec)
MariaDB [test]> CREATE TABLE t_mrg (
-> a INT,
-> b INT
-> ) ENGINE = MERGE,UNION=(t1,t2,t3);
Query OK, 0 rows affected (0.02 sec)
MariaDB [test]> INSERT INTO t1 VALUES (1,1);
Query OK, 1 row affected (0.02 sec)
MariaDB [test]> INSERT INTO t3 VALUES (2,2);
Query OK, 1 row affected (0.00 sec)
MariaDB [test]> SELECT a,b FROM t_mrg;
+------+------+
| a | b |
+------+------+
| 1 | 1 |
| 2 | 2 |
+------+------+
2 rows in set (0.00 sec)
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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Thank you. I'll add this info in the KB, because it doesnt seem obvious, for a user
No, really it doesn't include column names. MyISAM has no knowledge of column names and MERGE engine accesses MyISAM tables via the MyISAM API, so it also does not know not care about column names. Or Index names, for what it's worth.