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

RAND()()

RAND()()

  • RAND() is a MySQL math function: random 0–1. ORDER BY RAND() LIMIT 1 picks a random row (slow on huge tables). Use it in SELECT, e.g. SELECT RAND(marks) FROM students;
  • These functions do not change stored marks unless you UPDATE. NULL in, NULL out for most of them.
  • ORDER BY RAND() LIMIT 1 is the interview random-row trick. On a large table it is expensive — say that.
  • In a viva, one numeric example beats listing twenty functions.
  • On the example next to this theory: RAND()(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Technical Interview Tip: Explain RAND with one number. random 0–1. ORDER BY RAND() LIMIT 1 picks a random row (slow on huge tables).

Code Examples for RAND()()

RAND()() — sample query

-- RAND()()
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;

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

How to Explain RAND()() to an Interviewer

What is RAND?

random 0–1. ORDER BY RAND() LIMIT 1 picks a random row (slow on huge tables) Used in SELECT