Specifies a name for a column or table constraint. The name is
    used for a variety of purposes:

    o  The RDB$INTEG_FAIL error message specifies the name when an
       INSERT, UPDATE, or DELETE statement violates the constraint.

    o  The ALTER TABLE table-name DROP CONSTRAINT constraint-name
       statement specifies the name to delete a table constraint.

    o  The SHOW TABLE statements display the names of column and
       table constraints.

    o  The EVALUATING clause of the SET TRANSACTION and DECLARE
       TRANSACTION statements specifies constraint names.

    o  The ENABLE and DISABLE clauses of the ALTER and CREATE TABLE
       statements specify constraint names.

    o  The ALTER CONSTRAINT statement specifies constraint names.

    o  The DROP CONSTRAINT statement

    The CONSTRAINT clause is optional. If you omit the constraint
    name, SQL creates a name. However, Oracle Rdb recommends that
    you always name column and table constraints. If you supply a
    constraint name with the CONSTRAINT clause, it must be unique
    in the database or in the schema if you are using a multischema
    database.