SQL · Theory

Pivot Table

Theory

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Pivot Table

MySQL has no PIVOT keyword. You fake a pivot with SUM(CASE WHEN subject='Maths' THEN score END) AS maths, … GROUP BY roll. That turns rows into columns.

Fine for a few known subjects. Pain if subjects grow every week — keep a normalised marks table and pivot in the app.

Trap — inventing PIVOT syntax from SQL Server in a MySQL viva.

On the example next to this theory: Pivot Table: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

SUM(CASE WHEN subject='Maths' THEN score END) GROUP BY roll.

Pivot Table — sample query

-- Pivot Table
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;

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

Short notes

DefPivot = rows to columns. MySQL: CASE + GROUP BY.
RuleKnown list of columns. No PIVOT keyword.
TrapSQL Server PIVOT on MySQL.

-- Pivot Table 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;

Pivot Table

Pivot Table — sample query

Short notes

Questions

Pivot Table

Pivot Table — sample query

Short notes

Questions