The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.
SQL ALTER TABLE Syntax
To add a column in a table, use the following syntax:
ALTER TABLE table_name ADD column_name datatype
To delete a column in a table, use the following syntax (notice that some database systems don’t allow deleting a column):
ALTER TABLE table_name DROP COLUMN column_name
To change the data type of a column in a table, use the following syntax:
SQL Server / MS Access:
ALTER TABLE table_name ALTER COLUMN column_name datatype
My SQL / Oracle:
ALTER TABLE table_name MODIFY COLUMN column_name datatype
Oracle:
ALTER TABLE table_name MODIFY column_name datatype