SQL LEFT JOIN keyword tutorial

SQL LEFT JOIN keyword tutorial

The left join keyword returns all rows from the LEFT table (table_name1), even if there is no right table for the competition (table_name2 ).

SQL syntax added on the left

SELECT column_name(s)FROM table_name1LEFT JOIN table_name2 ON table_name1.column_name=table_name2.column_name

Let's take a look at the left join example?

 
 

  
  
 
   
 
    
Id
 
    
LastName
 
    
FirstName
 
    
Address
 
    
City
 
   
 
   
 
    
1
 
    
Hansen
 
    
Ola
 
    
Timoteivn 10
 
    
Sandnes
 
   
 
   
 
    
2
 
    
Svendson
 
    
Tove
 
    
Borgvn 23
 
    
Sandnes
 
   
 
   
 
    
3
 
    
Pettersen
 
    
Kari
 
    
Storgt 20
 
    
Stavanger
 
   
 
  
 
 

Let's take a look at the orders table.

 
 

  
  
 
   
 
    
O_Id
 
    
OrderNo
 
    
P_Id
 
   
 
   
 
    
1
 
    
77895
 
    
3
 
   
 
   
 
    
2
 
    
44678
 
    
3
 
   
 
   
 
    
3
 
    
22456
 
    
1
 
   
 
   
 
    
4
 
    
24562
 
    
1
 
   
 
   
 
    
5
 
    
34764
 
    
15
 
   
 
  
 
 

 
Now, we want to list all people and their orders-if any, from the above table.

We use the following SELECT statement:
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNoFROM PersonsLEFT JOIN OrdersON Persons.P_Id=Orders.P_IdORDER BY Persons.LastName
 
  
  

   
   
 
    
 
     
LastName
 
     
FirstName
 
     
OrderNo
 
    
 
    
 
     
Hansen
 
     
Ola
 
     
22456
 
    
 
    
 
     
Hansen
 
     
Ola
 
     
24562
 
    
 
    
 
     
Pettersen
 
     
Kari
 
     
77895
 
    
 
    
 
     
Pettersen
 
     
Kari
 
     
44678
 
    
 
    
 
     
Svendson
 
     
Tove
 
     
 
 
    
 
   
  
  
 
The left join keyword returns all rows from the LEFT table (persons), even if there is no competition right table (order ).