SQL JOINs Explained with Examples
JOINs combine rows from two tables based on a relationship. Here is a worked explanation of each join type with examples I keep coming back to. JOINs are how relational databases combine data from multiple tables. If you have ever struggled to remember the difference between a LEFT JOIN and a FULL OUTER JOIN, the issue is probably not the syntax but the mental model. I learned JOINs by working through concrete examples with two small tables, and that is the approach I will use here. Once you see the output of each join type on the same data, the distinctions stick. Setting Up the Example Tables Imagine two tables: customers and orders. Not every customer has placed an order, and not every order has a valid customer record due to a data import bug. This imperfect data is deliberate because clean data hides the differences between join types. CREATE TABLE customers ( id INT PRIMARY KEY, name VARCHAR(50) ); CREATE TABLE orders ( id INT PRIMARY KEY, customer_id INT, amount DECIMAL(10, 2) ); . customers: Alice(1), Bob(2), Carol(3), Dave(4) . orders: order for Alice, order for Bob, order for customer_id 99 (no such customer) INNER…