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ALTER TABLE: Add, Modify, Rename and Drop Columns
ALTER TABLE: Add, Modify, Rename and Drop Columns ALTER TABLE changes a table after it is made: add, change, rename or remove columns. ALTER TABLE students ADD phone VARCHAR(15); Shrinking a column (VARCHAR(100) → VARCHAR(10)) cuts long data. Check first: SELECT MAX(LENGTH(name)) FROM students;
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ALTER TABLE changes a table after it is made: add, change, rename or remove columns.
Example
ALTER TABLE students ADD phone VARCHAR(15);
Common mistake
Shrinking a column (VARCHAR(100) → VARCHAR(10)) cuts long data.
Check first: SELECT MAX(LENGTH(name)) FROM students;
| Want to | Use |
|---|---|
| New column | ADD COLUMN |
| Change type, size, NULL, DEFAULT | MODIFY COLUMN |
| Rename and change definition | CHANGE COLUMN old new type |
| Rename only | RENAME COLUMN old TO new |
| Remove column | DROP COLUMN |
Learn more in the lesson: 11.3 ALTER TABLE: Add, Modify, Rename and Drop Columns