To add, delete, or modify columns in an existing table. The ALTER TABLE statement is used.
To add a column in a table, the syntax is
ALTER TABLE table_name
ADD column_name datatype
To delete a column in a table, the syntax is
ALTER TABLE table_name
DROP COLUMN column_name
To change the data type of a column in a table, the syntax is
ALTER TABLE table_name
ALTER COLUMN column_name datatype
To change the data type of a column in a table My SQL / Oracle (prior version 10G):
ALTER TABLE table_name
MODIFY COLUMN column_name datatype
To change the data type of a column in a table Oracle 10G and later:
ALTER TABLE table_name
MODIFY column_name datatype