SELECT Processing Order

Written Order and Processing Order Differ

SQL is written with SELECT first, but processing starts with FROM. An aggregate query proceeds through FROM, WHERE, GROUP BY, HAVING, SELECT, ORDER BY, and LIMIT.

GOAL

Explain the logical order of the major clauses.

Which clause is processed immediately before GROUP BY?

CHECK IT

FROM customers

customers6 rows

name	city
Alice	Tokyo
Bob	Osaka
Carol	Tokyo
Dave	Osaka
Erin	Nagoya
Frank	NULL

An aggregate SELECT is processed in a different order from how it is written. FROM first reads all six customers rows.