Joins

Joins in SQL are nothing but a technique to join the two table based on a common field.

OrderID     CustomerID  OrderDate
10308           2      1996-09-18
10309           37    1996-09-19
10310           77    1996-09-20

CustomerID     CustomerName        ContactName           Country
1           Alfreds Futterkiste     Maria Anders          Germany
2          Ana Trujillo             Ana Trujillo          Mexico
3          Antonio Moreno           Antonio Moreno        Mexico

There are two tables

To join

SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
FROM Orders
INNER JOIN Customers
ON Orders.CustomerID=Customers.CustomerID; 

Then it shows this.

OrderID     CustomerName    OrderDate
10308     Ana Trujillo        9/18/1996
10365     Antonio Moreno      11/27/1996
10383     Around the Horn     12/16/1996
10355     Around the Horn     11/15/1996
10278     Berglunds snabbkp  8/12/1996

This can be result.

The join are of three types.

1.Inner join

2.Outer join

3.Self join