MCQ IN COMPUTER SCIENCE & ENGINEERING

Detailed explanation-1: -Constraints are the rules enforced on the data columns of a table. These are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the database.

Detailed explanation-2: -Enforcing key constraints, particularly on primary keys, can help the optimizer produce faster query plans, particularly for joins. When a primary key constraint is enforced on a table, the optimizer assumes that no rows in that table contain duplicate key values.

Detailed explanation-3: -Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint has a UNIQUE constraint automatically. However, you can have many UNIQUE constraints in a table, but only one PRIMARY KEY constraint can be there in one table.

Detailed explanation-4: -You can constrain any field or list of fields as unique. If a multiple-field constraint is designated as a unique key, the combined values of all fields in the index must be unique, even if two or more records have the same value in just one of the fields.

Detailed explanation-5: -Table constraints allow you to specify more than one column in a PRIMARY KEY, UNIQUE, CHECK, or FOREIGN KEY constraint definition. Column-level constraints (except for check constraints) refer to only one column. A constraint operates with the privileges of the owner of the constraint.