Interview preparation
SQL JOIN Interview Questions: The Complete Guide
The JOIN questions interviewers ask — inner, left, self, anti-join — with the NULL and duplicate pitfalls, and a practice path through real JOIN problems.
The JOIN patterns that recur
Left join with a NULL check (customers without orders, visits without transactions), self join for row-to-row comparisons (employees vs managers, rising temperature), and joins with aggregation (average process time per machine).
When you see two entities in the problem — customers and orders, employees and departments — the first step is deciding which table is the 'left' table and what the question counts.