What is a JOIN condition, and how is it specified?

Short answer: A JOIN condition specifies the columns that will be used to match rows between two or more tables. This condition typically uses ON or USING in SQL.

Example code

SELECT * FROM table1 JOIN table2 ON table1.id = table2.id; In this example, the condition table1.id = table2.id determines how the rows from both tables will be joined.

Real-world example (ShopNest)

An invoice query INNER JOINs Orders and OrderItems, and LEFT JOINs Discounts so orders without a coupon still appear.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.