SQL Joins

SQL JOIN

A conjoin article is use to fuse row from two or more defer, base on a interrelate column 'tween them.Let's face at a pick from the -Orders- defer:

OrderID	CustomerID	OrderDate

then, await at a excerption from the -Customers- table:

CustomerID	CustomerName	ContactName	Country

notification that the -CustomerID- pillar in the -Orders- table consult to the -CustomerID- in the -Customers- table. The relationship between the two table above is the -CustomerID- pillar.Then, we can create the follow SQL statement (that contain an inside conjoin), that select record that get mate values in both table:

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

 

Different type of SQL link

here are the different type of the articulation in SQL:

• (inner) join: return tape that accept twinned prise in both tabularise 

• Left (out) join: return all tape from the leave tabularise, and the fit tape from the correct tabularise 

• Right (out) join: return all tape from the correct tabularise, and the fit tape from the leave tabularise full (out)Full: return all tape when there is a match in either leave or correct tabularise

      

SQL INNER JOIN Keyword

The inside link keyword choose record that have equate value in both postpone.

inner join syntax

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

 

                                                      

SQL interior sum example The following SQL statement choose all order with client info:

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

 

unite trey defer The follow SQL statement take all rescript with client and shipper information:

SELECT Orders.OrderID, Customers.CustomerName, Shippers.ShipperName
FROM ((Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID)
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID);

SQL LEFT JOIN Keyword

SQL leave articulation Keyword The leave articulation keyword return all record from the left tabularise (tabularise1), and the meet record from the rectify tabularise (tabularise2). The termination is 0 record from 

the rectify side, if there is no touch.

LEFT JOIN Syntax : 

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

 note: In some databases database joint is visit database outer joint.