What is primary key with example in SQL?

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.

What is a good example of a primary key?

For example, students are routinely assigned unique identification (ID) numbers, and all U.S. citizens have government-assigned and uniquely identifiable Social Security numbers. Street addresses or driver license numbers are examples of primary keys used to uniquely identify (respectively) locations or cars.

What is primary key in mysql with example?

MySQL primary key is a single or combination of the field, which is used to identify each record in a table uniquely. If the column contains primary key constraints, then it cannot be null or empty. ... Primary Key vs. Unique Key.SNPrimary KeyUnique Key4.It creates a clustered index.It creates a non-clustered index.

How do I write a primary key in SQL query?

The syntax to create a primary key using the ALTER TABLE statement in SQL is: ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n); table_name.