MyISAM supports three different storage formats. Two of them, fixed and dynamic format, are chosen automatically depending on the type of columns you are using. The third, compressed format, can be created only with the myisampack utility.

When you use CREATE TABLE or ALTER TABLE for a table that has no BLOB or TEXT columns, you can force the table format to FIXED or DYNAMIC with the ROW_FORMAT table option.

You can decompress tables by specifying ROW_FORMAT=DEFAULT with ALTER TABLE.

See Section 13.1.8, “CREATE TABLE Syntax”, for information about ROW_FORMAT.