INNER JOIN

Two tables, one result, matched on the column they have in common

0 of 3 done · Lesson 6 of 8

Understand

The orders table records who placed each order as a number, because storing the customer name on every order would mean fixing it in six places when somebody changes their name. Useful for the database, useless for the person who asked you what Halcyon has been buying. A join puts the two tables back together for the length of one query, matching each order to the customer whose id it carries.

SELECT columns_from_either_table
FROM the_first_table
INNER JOIN the_second_table
ON what_makes_a_row_match;

SELECTwhich columns you wantFROMthe first tableINNER JOINthe table to bring inONwhat makes a row matchWHEREwhich rows to keep

The tables you are working with

5 rows

First rows of the customers table
id	name	city
1	Northwind	Auckland
2	Kea Ltd	Wellington
3	Halcyon	Auckland
4	Brightsmith	Dunedin

1 more row in the table. Your query sees all 5.

6 rows

First rows of the orders table
id	customer_id	item	amount
101	1	desk lamp	120
102	3	chair	340
103	1	monitor arm	210
104	5	filing box	65

2 more rows in the table. Your query sees all 6.