WL#4776: Alter Data Type
Affects: Server-9.x — Status: Un-Assigned — Priority: Very High
There is a new ALTER ... SET DATA TYPE clause in SQL:2008: ALTER TABLE table_name ALTER [ COLUMN ] column_name SET DATA TYPE data_type; This differs from ALTER ... MODIFY clause in MySQL 5.1: ALTER TABLE table_name MODIFY [COLUMN] col_name column_definition; It's more than a change in wording -- MySQL's idea of a "column definition" includes COMMENT, DEFAULT, NOT NULL, etc. So the standard-SQL clause is better if data type is the only thing one wants to change. Some details from SQL:2008 Foundation section <alter column data type clause>: * The ALTER should fail if the column is mentioned in a trigger, routine body, view, etc. * The new data type must be in the same category as the old one (for example exact numeric) and the new length must be greater than or equal to the old one. This is Non-Core Feature F382 "Alter column data type". References: BUG#42628 column comment deleted after changing charset/collation for column by statement [ Peter Gulutzan 2009-02-06 ]
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