Q. Define the various SQL Constraints.
Answer =
Constraints are the rules enforced on data or columns on a table. These are used to restrict the values that can be inserted in a table. This ensures data accuracy and reliability in the database.
Following are the most commonly used constraints available in SQL:
(a) NOT NULL Constraint: Ensures that a column cannot have NULL value.
(b) DEFAULT Constraint: Provides a default value for a column when no value is specified.
(c) UNIQUE Constraint: Ensures that all values in a column are unique. There should not be any redundant value in a column which is being restricted.
(d) PRIMARY Key: Uniquely identifies each row/record in a database table.
(e) FOREIGN Key: Uniquely identifies a row/record in any other database table.
(f) CHECK Constraint: The CHECK constraint ensures that all values in a column satisfy certain conditions. For example, to restrict the salary column that it should contain salary more than 10,000.
Following are the most commonly used constraints available in SQL:
(a) NOT NULL Constraint: Ensures that a column cannot have NULL value.
(b) DEFAULT Constraint: Provides a default value for a column when no value is specified.
(c) UNIQUE Constraint: Ensures that all values in a column are unique. There should not be any redundant value in a column which is being restricted.
(d) PRIMARY Key: Uniquely identifies each row/record in a database table.
(e) FOREIGN Key: Uniquely identifies a row/record in any other database table.
(f) CHECK Constraint: The CHECK constraint ensures that all values in a column satisfy certain conditions. For example, to restrict the salary column that it should contain salary more than 10,000.
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