SIGN()() — SQL Technical Interview Questions & Answers

SIGN()()

SIGN()()

  • SIGN() is a MySQL math function: negative -1, zero 0, positive 1. Use it in SELECT, e.g. SELECT SIGN(marks) FROM students;
  • These functions do not change stored marks unless you UPDATE. NULL in, NULL out for most of them.
  • Trap: mixing SIGN with TRUNCATE TABLE (different word). Trap: maths on VARCHAR without CAST.
  • In a viva, one numeric example beats listing twenty functions.
  • On the example next to this theory: SIGN()(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Technical Interview Tip: Explain SIGN with one number. negative -1, zero 0, positive 1.

Code Examples for SIGN()()

SIGN()() — sample query

-- SIGN()()
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;

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

How to Explain SIGN()() to an Interviewer

What is SIGN?

negative -1, zero 0, positive 1 Used in SELECT