Restrictions on Referential Constraints

You must have the References privilege to create a referential constraint.

When you use the REFERENCES clause, you must observe the following restrictions:

• The referenced and referencing tables must be in the same database.
• The referenced column (or set of columns when you use the multiple-column constraint format) must have a unique or primary-key constraint.
• The data types of the referencing and referenced columns must be identical.

  The only exception is that a referencing column must be an integer data type if the referenced column is a SERIAL or SERIAL8 data type.

• You cannot place a referential constraint on a BYTE or TEXT column.
• You cannot place a referential constraint on a BLOB or CLOB column.
• When you use the single-column constraint format, you can reference only one column.
• In Dynamic Server, when you use the multiple-column constraint format, the maximum number of columns in the REFERENCES clause is 16, and the total length of the columns cannot exceed 390 bytes if the page size is 2 kilobytes. (The maximum length increases with the page size.)
• In Extended Parallel Server, when you use the multiple-column constraint format, the maximum number of columns in the REFERENCES clause is 16, and the total length of the columns cannot exceed 380 bytes.