Using Check Constraints to Simulate Domains

(Craig S. Mullins) All of the popular RDBMS products provide table check constraints: Oracle, Informix, DB2, Sybase, and Microsoft SQL Server. Check constraints enable enhanced data integrity without requiring procedural logic (such as in stored procedures and triggers). Let’s examine the basics of relational table check constraints.

A constraint is basically a restriction placed upon the data values that can be stored in a column or columns of a table. Of course, RDBMS products have provided several different types of constraints for a long time now. This includes referential constraints (to define primary and foreign keys) and unique constraints (to prohibit duplicates).