Interval — SQL Technical Interview Questions & Answers

Interval

Interval

  • Interval (DATE_INTERVAL) is a MySQL date/time helper. Dates are stored in DATE / DATETIME / TIMESTAMP columns. Always quote literals: '2026-08-19'.
  • Typical pattern: SELECT DATE_INTERVAL(…); or SELECT DATE_INTERVAL(dob) FROM students; NOW() / CURDATE() / CURTIME() have empty brackets — they read the clock.
  • DATE_FORMAT(dob, '%d-%b-%Y') is for display. DATEDIFF(end, start) is days between. INTERVAL 7 DAY is how you add a week: DATE_ADD(CURDATE(), INTERVAL 7 DAY).
  • Trap: comparing dates as VARCHAR. Trap: TIMESTAMP vs DATETIME timezone stories — DATETIME is ‘wall clock’, TIMESTAMP is UTC-stored (say this only if asked).
  • On the example next to this theory: Interval: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Technical Interview Tip: DATE_INTERVAL: one SELECT example. Quote 'YYYY-MM-DD'.

Code Examples for Interval

Interval — sample query

-- Interval
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;

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

How to Explain Interval to an Interviewer

What is DATE_INTERVAL?

Date/time function for Interval Use in SELECT on a DATE column

Current datetime?

NOW() or CURRENT_TIMESTAMP