12-7-2010 12:44:22
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:
ALTER TABLE table_name
ALTER COLUMN column_name datatype

(copy http://www.w3schools.com/sql/sql_alter.asp)