The data type determines the kind of values that users can store in the field. Like every programming languages, the SQL also has specific data type to store data. Following are some data type and there descriptions in which SQL allows us to store data.

Microsoft Access Data Types

Source: Microsoft Access Help

The AUTO INCREMENT generates a new number that increment by 1 from the previous number. This will allow a unique number to be associated in a row when it is inserted into a table.

You can set the AUTO INCREMENT during creation of the table or you can also use ALTER TABLE Statement if you have already created the table.

The following example will create a table named "Users" and add a Primary Key with Auto Increment in ID field.

Syntax for SQL Server

The ALTER TABLE statement is used to change the structure of an existing table like adding, deleting, or modifying of column.

SQL ALTER TABLE Syntax

To add a new column to the existing table use the following syntax: