What is a primary key in SQL?

Question

The PRIMARY KEY constraint uniquely identifies each record in a table. 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).

What is primary key in SQL with example?

A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values. A table can have only one primary key, which may consist of single or multiple fields.

What is primary key and example?

A primary key is a column -- or a group of columns -- in a table that uniquely identifies the rows in that table. For example, in the table below, CustomerNo, which displays the ID number assigned to different customers, is the primary key. CUSTOMERS. CustomerNo. FirstName.

What is a primary key explain?

A primary key is the column or columns that contain values that uniquely identify each row in a table. A database table must have a primary key for Optim to insert, update, restore, or delete data from a database table.

What are the 5 types of primary key?

Let's look at each of them separately.Primary Key. A primary key is a column of a table or a set of columns that helps to identify every record present in that table uniquely. ... Super Key. ... Candidate Key. ... Alternate Key. ... Foreign Key. ... Composite Key. ... Unique Key.7 Types of Keys in DBMS Explained | upGrad blog

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