The single-column constraint format cannot specify a constraint that involves more than one column. Thus, you cannot use the single-column constraint format to define a composite key. For information on multiple-column constraints, see Multiple-Column Constraint Format.
You cannot place unique, primary-key, or referential constraints on BYTE or TEXT columns. You can, however, check for NULL or non-NULL values with a check constraint.
You cannot place unique constraints, primary-key constraints, or referential constraints on BLOB or CLOB columns of Dynamic Server.
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