What are the SQL constraints? Ans: SQL constraints  are used to specify rules for the data in a table.  Constraints  are used to limit the type of data that can go into a table   1.      NOT NULL Constraint  − Ensures that a column cannot have NULL value. 2.      DEFAULT Constraint  − Provides a default value for a column when none is specified. 3.      UNIQUE Constraint  − Ensures that all values in a column are different. 4.      PRIMARY Key  − Uniquely identifies each row/record in a database table. 5.      FOREIGN Key  − Uniquely identifies a row/record in any of the given database table. 6.      CHECK Constraint  − The CHECK constraint ensures that all the values in a column satisfies certain conditions. 7.      INDEX  − Used to create and retrieve data from the database very qu...