Module 8intermediate

SQL Joins

Lessons

INNER JOIN

1 / 2

INNER JOIN returns only rows that have matching values in both tables.

Syntax

text-blue-600 dark:text-blue-400 font-semibold">SELECT columns text-blue-600 dark:text-blue-400 font-semibold">FROM table1 INNER text-blue-600 dark:text-blue-400 font-semibold">JOIN table2 text-blue-600 dark:text-blue-400 font-semibold">ON table1.column = table2.column;

Sample Tables Used in This Course

employeesEmployee records

Column	Type	Key
id	INTEGER	PK
name	TEXT
department	TEXT
salary	INTEGER
country	TEXT
manager_id	INTEGER	FK → employees.id
email	TEXT
hire_date	TEXT

Sample Data (first 5 rows)

id	name	department	salary	country	manager_id	email	hire_date
1	Ahmed Al-Thani	IT	25000	Qatar	NULL	ahmed@qatarco.qa	2018-03-15
2	Fatima Al-Kuwari	HR	18000	Qatar	1	fatima@qatarco.qa	2019-06-01
3	Mohammed Al-Sulaiti	Finance	22000	Qatar	1	mohammed@qatarco.qa	2017-09-20
4	Sara Al-Mansouri	IT	20000	Qatar	1	sara@qatarco.qa	2020-01-10
5	Khalid Hassan	IT	17000	Egypt	4	khalid@qatarco.qa	2021-04-05

ordersOrder transactions

Column	Type	Key
id	INTEGER	PK
customer_id	INTEGER	FK → customers.id
amount	DECIMAL
order_date	TEXT
region	TEXT
status	TEXT

Sample Data (first 5 rows)

id	customer_id	amount	order_date	region	status
1	1	15000	2024-01-15	Doha	completed
2	2	8500	2024-01-20	Doha	completed
3	3	22000	2024-02-01	Doha	pending
4	1	5000	2024-02-10	Al Wakrah	completed
5	4	12000	2024-02-15	Lusail	shipped

Relationships: Primary Keys (PK) uniquely identify rows. Foreign Keys (FK) reference other tables.

Practice with these tables in the SQL Console. Click "Open Console" in the sidebar.

Example

text-blue-600 dark:text-blue-400 font-semibold">SELECT orders.order_id, customers.name, orders.amount
text-blue-600 dark:text-blue-400 font-semibold">FROM orders
INNER text-blue-600 dark:text-blue-400 font-semibold">JOIN customers text-blue-600 dark:text-blue-400 font-semibold">ON orders.customer_id = customers.id;

Combines order info with customer names

Learning Objectives

Understand INNER JOIN
Understand LEFT JOIN
Join tables on foreign keys

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