SQL LEFT JOIN keyword tutorial

Source: Internet
Author: User

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 ).

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