DECIMAL — SQL Technical Interview Questions & Answers

DECIMAL

DECIMAL

  • DECIMAL(10,2) is exact: 10 digits, 2 after the point — money, percentages you must not round wrongly. FLOAT/DOUBLE are approximate binary. Banks and fees: DECIMAL.
  • 10,2 means 8 digits before the point + 2 after (total 10). Don’t guess — say ‘precision and scale’.
  • Trap: FLOAT for salary.
  • On the example next to this theory: DECIMAL: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Technical Interview Tip: fee DECIMAL(10,2) NOT NULL

Code Examples for DECIMAL

DECIMAL — sample query

-- DECIMAL
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;

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

How to Explain DECIMAL to an Interviewer

Why DECIMAL for money?

Exact decimal FLOAT rounds badly