Add/Delete Column — SQL Technical Interview Questions & Answers

Add/Delete Column

Add/Delete Column

  • Add: ALTER TABLE students ADD COLUMN city VARCHAR(40); Delete: ALTER TABLE students DROP COLUMN city; DROP COLUMN throws that data away.
  • Add AFTER marks if you care about column order (optional). Apps that SELECT * will see the new column — better to list columns in production SQL.
  • Trap: DROP COLUMN used by a live INSERT. Trap: ADD without a type.
  • On the example next to this theory: Add/Delete Column — aLTER TABLE changes structure without rebuilding the whole table.

Technical Interview Tip: ADD COLUMN city VARCHAR(40); DROP COLUMN city;

Code Examples for Add/Delete Column

Add/Delete Column — sample query

CREATE TABLE items (id INTEGER PRIMARY KEY, title TEXT);
ALTER TABLE items ADD COLUMN price REAL DEFAULT 0;
INSERT INTO items (id, title, price) VALUES (1, 'Pen', 10);
SELECT * FROM items;

Add/Delete Column — aLTER TABLE changes structure without rebuilding the whole table.

How to Explain Add/Delete Column to an Interviewer

How do you remove a column?

ALTER TABLE students DROP COLUMN city;