SQL · Theory

SIGN()()

Theory

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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.

Exam tip

Explain SIGN with one number. negative -1, zero 0, positive 1.

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.

Short notes

DefSIGN() — negative -1, zero 0, positive 1.
RuleSELECT the function; UPDATE only if you mean to store it.
TrapNULL in → NULL out. Don’t confuse with table TRUNCATE.

-- 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()()

SIGN()() — sample query

Short notes

Questions

SIGN()()

SIGN()() — sample query

Short notes

Questions