To add a column to an existing table, the database administrator should use the ALTER TABLE statement with the ADD COLUMN clause. This statement allows modifying the structure of a table by adding, deleting, or changing columns and constraints. The CREATE statement is used to create a new table, not to modify an existing one. The UPDATE statement is used to modify the data in a table, not the structure. The DROP statement is used to delete a table or a column, not to add a new column. References:
CompTIA IT Fundamentals (ITF+) Certification Guide, page 307
SQL ADD COLUMN - Add One or More Columns To a Table