SQL LEFT JOIN
What is a LEFT JOIN in SQL?
A LEFT JOIN performs a join starting with the first (left-most) table.
Then, any matched records from the second table (right-most) will be included.
LEFT JOIN and LEFT OUTER JOIN are the same.

The SQL LEFT JOIN syntax
The general LEFT JOIN syntax is
SELECT column-names FROM table-name1 LEFT JOIN table-name2 ON column-name1 = column-name2 WHERE condition
The general LEFT OUTER JOIN syntax is
SELECT column-names FROM table-name1 LEFT OUTER JOIN table-name2 ON column-name1 = column-name2 WHERE condition
ORDER |
---|
Id |
OrderDate |
OrderNumber |
CustomerId |
TotalAmount |
CUSTOMER |
---|
Id |
FirstName |
LastName |
City |
Country |
Phone |
SQL LEFT JOIN Example
Problem: List all customers and the
total amount they spent irrespective
whether they placed any orders
or not.
total amount they spent irrespective
whether they placed any orders
or not.
SELECT OrderNumber, TotalAmount, FirstName, LastName, City, Country FROM Customer C LEFT JOIN [Order] O ON O.CustomerId = C.Id ORDER BY TotalAmount
Note: The ORDER BY TotalAmount shows the customers without orders first (i.e. TotalMount is NULL).
Result: 832 records
OrderNumber | TotalAmount | FirstName | LastName | City | Country |
---|---|---|---|---|---|
NULL | NULL | Diego | Roel | Madrid | Spain |
NULL | NULL | Marie | Bertrand | Paris | France |
542912 | 12.50 | Patricio | Simpson | Buenos Aires | Argentina |
542937 | 18.40 | Paolo | Accorti | Torino | Italy |
542897 | 28.00 | Pascale | Cartrain | Charleroi | Belgium |
542716 | 28.00 | Maurizio | Moroni | Reggio Emilia | Italy |
543028 | 30.00 | Yvonne | Moncada | Buenos Aires | Argentina |
543013 | 36.00 | Fran | Wilson | Portland | USA |
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