13.1.10.3 Silent Column Specification Changes

In some cases, MySQL silently changes column specifications from those given in a CREATE TABLE or ALTER TABLE statement. These might be changes to a data type, to attributes associated with a data type, or to an index specification.

All changes are subject to the internal row-size limit of 65,535 bytes, which may cause some attempts at data type changes to fail. See Section E.7.4, “Limits on Table Column Count and Row Size”.

Some silent column specification changes include modifications to attribute or index specifications:

Possible data type changes are given in the following list. If a version number is given, the change occurs only up to the versions listed. After that, an error occurs if a column cannot be created using the specified data type.

To see whether MySQL used a data type other than the one you specified, issue a DESCRIBE or SHOW CREATE TABLE statement after creating or altering the table.

Certain other data type changes can occur if you compress a table using myisampack. See Section 14.1.3.3, “Compressed Table Characteristics”.