SQL LEFT JOIN
SQL LEFT JOIN returns all the rows from the left table mentioned with the LEFT JOIN clause. If there are no matching rows in right table then output rows will return NULL values.
FROM Table1 LEFT JOIN Table2
ON Table1.columnName = Table2.columnName
Refer below image to understand LEFT JOIN, here green part is output for LEFT JOIN.
Here we will consider one example for LEFT JOIN condition where we will use two tables named as SalesDetails and ClientDetails.
Table Name: SalesDetails
Table Name: ClientDetails
As you can see, first table has 8 records and second table has 10 records. From above two tables, we need columns OrderID and OrderDate from SalesDetails table and one column ClientName from ClientDetails table and sorted in ascending order by OrderDate column. So to get the output from two tables we will use LEFT JOIN query as given below.
SELECT SalesDetails.OrderID, ClientDetails.ClientName, SalesDetails.OrderDate FROM SalesDetails LEFT JOIN ClientDetails ON SalesDetails.ClientID = ClientDetails.ClientID ORDER BY OrderDate
So, in LEFT JOIN all the records are returned from the table which is mentioned in left side.
Reference: Manzoor Siddiqui [www.SQLServerLog.com]