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

TRUNCATE()()

TRUNCATE()()

  • TRUNCATE() is a MySQL math function: TRUNCATE(x, d) cuts decimals without rounding — not TRUNCATE TABLE. Use it in SELECT, e.g. SELECT TRUNCATE(marks) FROM students;
  • These functions do not change stored marks unless you UPDATE. NULL in, NULL out for most of them.
  • Trap: mixing TRUNCATE 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: TRUNCATE()() — dELETE removes matching rows. TRUNCATE clears a whole table faster (MySQL).

Technical Interview Tip: Explain TRUNCATE with one number. TRUNCATE(x, d) cuts decimals without rounding — not TRUNCATE TABLE.

Code Examples for TRUNCATE()()

TRUNCATE()() — sample query

CREATE TABLE tags (id INTEGER PRIMARY KEY, label TEXT);
INSERT INTO tags VALUES (1, 'old'), (2, 'keep');
DELETE FROM tags WHERE label = 'old';
SELECT * FROM tags;

TRUNCATE()() — dELETE removes matching rows. TRUNCATE clears a whole table faster (MySQL).

How to Explain TRUNCATE()() to an Interviewer

What is TRUNCATE?

TRUNCATE(x, d) cuts decimals without rounding — not TRUNCATE TABLE Used in SELECT