What Are SQL Constraints ? SQL constraints are rules applied to columns or tables in a relational database to limit the type of data that can be inserted, updated, or deleted. Synonyms for CONSTRAINT : restraint, discipline, repression, inhibition, suppression, composure, discretion, self-control; Antonyms of CONSTRAINT : incontinence ... Learn the meaning of constraint as a noun in English, with examples of usage and synonyms. Find out how to use constraint in different contexts, such as business, academic and everyday situations. This journal provides a common forum for the many disciplines interested in constraint programming and constraint satisfaction and optimization, and the many ...