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OPTION Loop Join in SQL Server

The OPTION ( LOOP JOIN ) would enforce LOOP JOIN across all joins in the query. Using the OPTION ( LOOP JOIN ) appears to allows the query optimizer to join the tables using the nested loops in which ever order SQL server decides it is optimal. The OPTION clause must be a last clause in a statement. The syntax is,
OPTION ( LOOP JOIN );

Now, Lets see how to use LOOP JOIN with SELECT statement.?

select *from tbl_EmployeeDetails as e
inner join tbl_BankDetails as b on b.EmpID=e.Id
inner join tbl_SalesDetails as s on s.BankId=b.Id
OPTION(LOOP JOIN);

The statement returned execution plan is,


The above statement loops through all the joins that starts from sales details and goes by bank details to employee details in which the order that SQL server thinks it is optimal. This does not follow the order of joins that we specify. Suppose, if you want the SQL server to follow the order of joins that you specify you have to use FORCE ORDER in OPTION clause.

However, the two types of query hints cannot be mixed in a statement. Suppose, if you attempt to do so you will get an 1042 error.

select *from tbl_EmployeeDetails as e
inner join tbl_BankDetails as b on b.EmpID=e.Id
inner MERGE join tbl_SalesDetails as s on s.BankId=b.Id
OPTION(LOOP JOIN);

In this statement we are using both MERGE and LOOP JOIN query hint that you can see in the above statement that causes the 1042 error. The statement returned result is,
















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