IFNULL() — SQL Technical Interview Questions & Answers

IFNULL()

IFNULL()

  • IFNULL(marks, 0) returns marks if not NULL, else 0. Two arguments only. COALESCE(a,b,c) walks the list. In SELECT lists IFNULL is the student favourite.
  • Trap: IFNULL as a WHERE — you usually still want IS NULL for ‘missing’ vs 0.
  • On the example next to this theory: IFNULL(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Technical Interview Tip: IFNULL(marks, 0). COALESCE(marks, bonus, 0).

Code Examples for IFNULL()

IFNULL() — sample query

-- IFNULL()
CREATE TABLE demo (
  id INTEGER PRIMARY KEY,
  label TEXT NOT NULL,
  qty INTEGER DEFAULT 0
);
INSERT INTO demo (id, label, qty) VALUES
  (1, 'alpha', 2),
  (2, 'beta', 5);
SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

IFNULL(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

How to Explain IFNULL() to an Interviewer

IFNULL vs COALESCE?

IFNULL two args COALESCE many args