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SQL Server: ALTER TABLE Statement

ALTER TABLE statement

This SQL Server tutorial explains how to use the ALTER TABLE statement in SQL Server (Transact-SQL) to add a column, modify a column, drop a column, rename a column or rename a table with syntax and examples.

Description

The SQL Server (Transact-SQL) ALTER TABLE statement is used to add, modify, or drop columns in a table.

Add column in table

You can use the ALTER TABLE statement in SQL Server to add a column to a table.

Syntax

The syntax to add a column in a table in SQL Server (Transact-SQL) is:

ALTER TABLE table_name
  ADD column_name column_definition;

Example

Let’s look at an example that shows how to add a column in an SQL Server table using the ALTER TABLE statement.

For example:

ALTER TABLE employees
  ADD last_name VARCHAR(50);

This SQL Server ALTER TABLE example will add a column to the employees table called last_name.

Add multiple columns in table

You can use the ALTER TABLE statement in SQL Server to add multiple columns to a table.

Syntax

The syntax to add multiple columns to an existing table in SQL Server (Transact-SQL) is:

ALTER TABLE table_name
  ADD column_1 column_definition,
      column_2 column_definition,
      ...
      column_n column_definition;

Example

Let’s look at an example that shows how to add multiple columns to a table in SQL Server using the ALTER TABLE statement.

For example:

ALTER TABLE employees
  ADD last_name VARCHAR(50),
      first_name VARCHAR(40);

This SQL Server ALTER TABLE example will add two columns, last_name as a VARCHAR(50) field and first_name as a VARCHAR(40) field to the employees table.

Modify column in table

You can use the ALTER TABLE statement in SQL Server to modify a column in a table.

Syntax

The syntax to modify a column in an existing table in SQL Server (Transact-SQL) is:

ALTER TABLE table_name
  ALTER COLUMN column_name column_type;

Example

Let’s look at an example that shows how to modify a column in a table in SQL Server using the ALTER TABLE statement.

For example:

ALTER TABLE employees
  ALTER COLUMN last_name VARCHAR(75) NOT NULL;

This SQL Server ALTER TABLE example will modify the column called last_name to be a data type of VARCHAR(75) and force the column to not allow null values.

Drop column in table

You can use the ALTER TABLE statement in SQL Server to drop a column in a table.

Syntax

The syntax to drop a column in an existing table in SQL Server (Transact-SQL) is:

ALTER TABLE table_name
  DROP COLUMN column_name;

Example

Let’s look at an example that shows how to drop a column in a table in SQL Server using the ALTER TABLE statement.

For example:

ALTER TABLE employees
  DROP COLUMN last_name;

This SQL Server ALTER TABLE example will drop the column called last_name from the table called employees.

Rename column in table

You can not use the ALTER TABLE statement in SQL Server to rename a column in a table. However, you can use sp_rename, though Microsoft recommends that you drop and recreate the table so that scripts and stored procedures are not broken.

Syntax

The syntax to rename a column in an existing table in SQL Server (Transact-SQL) is:

sp_rename 'table_name.old_column_name', 'new_column_name', 'COLUMN';

Example

Let’s look at an example that shows how to rename a column in a table in SQL Server using sp_rename.

For example:

sp_rename 'employees.last_name', 'lname', 'COLUMN';

This SQL Server example will use sp_rename to rename the column in the employees table from last_name to lname.

Rename table

You can not use the ALTER TABLE statement in SQL Server to rename a table. However, you can use sp_rename, though Microsoft recommends that you drop and recreate the table so that scripts and stored procedures are not broken.

Syntax

The syntax to rename a table in SQL Server (Transact-SQL) is:

sp_rename 'old_table_name', 'new_table_name';

Example

Let’s look at an example that shows how to rename a table in SQL Server using sp_rename.

For example:

sp_rename 'employees', 'emps';

This SQL Server example will use sp_rename to rename the employees table to emps.

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