Types of constraints in sql They refer to the column which they are following. If a column has CREATE INDEX constraint, it's faster to retrieve data if we use that column for data retrieval. SQL key constraints are used to specify rules for the data in a table. NOT NULL Constraint; UNIQUE KEY Constraint; Default Constraint; CHECK KEY Constraint; PRIMARY KEY Constraint; FOREIGN KEY Constraint. This ensures the accuracy and reliability of the data in the table. A not-null constraint defines that a column should never be a null value. Constraints that are directly applied in the schemas of the data model, by specifying them in the DDL(Data Definition Language). To avoid errors resulting from this ambiguity, rewrite the constraint using the TO_DATE function with a four-digit year. RELY. Domain constraints are a type of integrity constraint that ensure the values stored in a column (or attribute) of a database are valid and within a specific range or domain. osmqolubfvyuwqkhygmrhmwvodfdnstffjufeljrnoquziwedmefuaapxgdhhorrygjr