SQL ALTER Keyword

ALTER TABLE

The ALTER TABLE command adds, deletes, or modifies columns in a table.

The ALTER TABLE command also adds and deletes various constraints in a table.

The following SQL adds an "Email" column to the "Customers" table:

ALTER TABLE Customers
ADD Email varchar(255);

The following SQL deletes the "Email" column from the "Customers" table:

ALTER TABLE Customers
DROP COLUMN Email;

The ALTER COLUMN command is used to change the data type of a column in a table.

The following SQL changes the data type of the column named "BirthDate" in the "Employees" table to type year:

ALTER TABLE Employees
ALTER COLUMN BirthDate year;