Constraint Names That the Database Server Generates

constraint_typetabid_constraintid 

In this template, constraint_type is the letter u for unique or primary-key constraints, r for referential constraints, c for check constraints, and n for NOT NULL constraints. In the template, tabid and constraintid are values from the tabid and constrid columns of the systables and sysconstraints system catalog tables, respectively. For example, the constraint name for a unique constraint might look like ? u111_14? (with a leading blank space).

If the generated name conflicts with an existing identifier, the database server returns an error, and you must then supply an explicit constraint name.

[blankspace]tabid__constraintid

For example, the index name might be something like " 111_14 " (quotation marks used here to show the blank space).