Question

Constraints can be added after the table creation by using which statement?

a) DELETE TABLE
b) ALTER TABLE
c) CREATE CONSTRAINT
d) MODIFY TABLE

Answer 1

Constraints can be added to an existing database table using the ALTER TABLE SQL statement. It allows modification like adding primary keys, foreign keys, and other constraints ensuring the table data conforms to these new rules.

Step-by-step explanation:

Constraints can be added to an existing table after its creation by using the ALTER TABLE statement. This SQL command is used to modify the structure of an existing table within the database. It allows you to add new constraints, such as primary keys, foreign keys, unique constraints, check constraints, etc.

For example, to add a primary key constraint to an existing table:

ALTER TABLE table_name
ADD CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ...);

It is important to note that when adding a constraint with ALTER TABLE, you must ensure that existing table data conforms to the new constraint or the database system will reject the change.