SQL Cheat Sheet for Placements — Quick Revision

The SQL you need for online tests and interviews.

Order of a query

Written: SELECT → FROM → WHERE → GROUP BY → HAVING → ORDER BY → LIMIT

Run: FROM / JOIN → WHERE → GROUP BY → HAVING → SELECT → DISTINCT → ORDER BY → LIMIT

That’s why a SELECT alias can’t be used in WHERE, but can be used in ORDER BY.

Join	Returns
INNER	Rows that match in both
LEFT	All left rows; NULLs where there’s no match
RIGHT	All right rows
FULL OUTER	All rows from both
CROSS	Every pair of rows
SELF	A table joined to itself

Rows with no match: LEFT JOIN b ... WHERE b.id IS NULL, or NOT EXISTS.