SQL Server Execution Plans - Red Gate Software

Chapter 4: Understanding More Complex Query Plans
The introduction of this new functionality changes the execution plan substantially, as
shown in Figure 4.6.
Figure 4.6
The TOP statement is now be applied row by row within the control of the APPLY
function, so the second Index Scan against the ProductListPriceHistory table,
and the Merge Join that joined the tables together, are no longer needed. Furthermore,
only the Index Seek and Top operations are required to provide data back for the
Nested Loops operation.
So, which method of writing this query do you think is the most efficient? One way
to find out is to run each query with the SET STATISTICS IO option set to ON. With
this option set, SQL Server displays I/O statistics as part of the Messages returned by
the query.
When we run the first query, which uses the sub-select, the results are:
(293 row(s) affected)
Table 'ProductListPriceHistory'. Scan count 396, logical reads 795
Table 'Product'. Scan count 1, logical reads 15, physical reads 0
If we run the query using a derived table, the results are:
(293 row(s) affected)
Table 'ProductListPriceHistory'. Scan count 504, logical reads 1008
Table 'Product'. Scan count 1, logical reads 15, physical reads 0,
146