SQL Server Execution Plans - Red Gate Software

Figure 5.7
Chapter 5: Controlling Execution Plans with Hints
As you can see, the query uses a mix of Nested Loops and Hash Match operators to put
the data together, and it runs in around 214ms. Now, let's view the I/O output of the
query. This can be done by navigating from the main menu, Query | Query Options,
selecting the Advanced tab and selecting the Set Statistics I/O check box.
Table 'Illustration'. Scan count 1, logical reads 273…
Table 'ProductModelIllustration'. Scan count 1, logical reads 183…
Table 'Worktable'. Scan count 0, logical reads 0…
Table 'ProductModel'. Scan count 1, logical reads 14…
Table 'Product'. Scan count 1, logical reads 15…
Listing 5.8
Most of the reads come from the Illustration and ProductModelIllustration
tables. It occurs to you that allowing the query to perform all those Hash Match join
operations may be slowing it down because of the reads and writes in tempdb, so you
decide to change the behavior by adding the LOOP JOIN hint to the end of the query.
OPTION ( LOOP JOIN );
Listing 5.9
186