SQL ALTER Keyword
ALTER TABLE command adds, deletes, or
modifies columns in a table.
ALTER TABLE command also adds and
deletes various constraints in a table.
The following SQL adds an "Email" column to the "Customers" table:
ADD Email varchar(255);
The following SQL deletes the "Email" column from the "Customers" table:
DROP COLUMN Email;
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 COLUMN BirthDate year;