MCQ IN COMPUTER SCIENCE & ENGINEERING

Detailed explanation-1: -A primary key is a column of table which uniquely identifies each tuple (row) in that table. Primary key enforces integrity constraints to the table. Only one primary key is allowed to use in a table. The primary key does not accept the any duplicate and NULL values.

Detailed explanation-2: -Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).

Detailed explanation-3: -Primary Key is a column that is used to uniquely identify each tuple of the table. It is used to add integrity constraints to the table. Only one primary key is allowed to be used in a table. Duplicate and NULL (empty) values are not valid in the case of the primary key.

Detailed explanation-4: -Key Difference between Primary Key and Unique key Primary key does not allow null columns, whereas the Unique key allows null columns. In the primary key, duplicate keys are not allowed, while in a unique key, if one or more key parts are null, then duplicate keys are allowed.

Detailed explanation-5: -This unique standard attribute is called a primary-key attribute. The primary-key attribute and a value assigned to a record becomes the primary key of the record. Every record added to the data store must have a primary key. The primary-key attribute type can be of any supported Dgraph property types.