MERGE Table Problems
The following are known problems with MERGE tables:
• In versions of MySQL Server prior to 5.1.23, it was possible to create temporary merge tables with
nontemporary child MyISAM tables.
From versions 5.1.23, MERGE children were locked through the parent table. If the parent was
temporary, it was not locked and so the children were not locked either. Parallel use of the MyISAM
tables corrupted them.
• If you use ALTER TABLE to change a MERGE table to another storage engine, the mapping to the
underlying tables is lost. Instead, the rows from the underlying MyISAM tables are copied into the
altered table, which then uses the specified storage engine.
• The INSERT_METHOD table option for a MERGE table indicates which underlying MyISAM table to use
for inserts into the MERGE table. However, use of the AUTO_INCREMENT table option for that MyISAM
table has no effect for inserts into the MERGE table until at least one row has been inserted directly
into the MyISAM table.
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