SQL Joins (INNER JOIN Tutorial)

SQL joins are used when you want to combine rows from more than one table in a database. A JOIN is a means of combining fields from two or more tables by using a common field.

First things first, before I show you an example, I will tell you the most common types SQL JOINs you can have:

INNER JOIN:
This will return all rows when there is at least one match in both tables.
LEFT JOIN: This will return all rows from the left table, and the matched rows from the right table.
RIGHT JOIN:
This will return all rows from the right table, and the matched rows from the left table.
FULL JOIN:
This will return all rows when there is a match in at least one of the tables.

The most common type of all the JOINS is the INNER JOIN or a simple join. This is the example I will be showing you more of today.

Table 1: Customer ID Name 1 Walmurt 2 Turgat 3 Mojulrs 4 Kroogers

Table 2: Orders CustomerID OrderID Date Amount 2 1001 1-1-2015 $100 4 1002 1-4-2015 $400 2 1003 1-6-2015 $200 3 1004 1-6-2015 $100

Now, lets JOIN these two tables with a SQL Select Statement.

Select Customer.ID as CustomerID, Name, OrderID, Date, Amount from Customer
INNER JOIN
Orders on Orders.CustomerID = Customer.ID;

The results to this statement will produce the results below.
CustomerID	Name	OrderID	Date	Amount
2	Turgat	1001	1-1-2015	$100
4	Kroogers	1002	1-4-2015	$400
2	Turgat	1003	1-6-2015	$200
3	Mojulrs	1004	1-6-2015	$100

Please note, several operators can be used to join tables, such as =, <, >, <>, <=, >=, BETWEEN, LIKE, and NOT, just to name a few. However, the most common operator is the equal symbol.


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