SQL Server Team-based Development - Red Gate Software

Chapter 11: SQL Refactoring
same as a table scan) instead of a possible index seek, thus possibly increasing I/O reads
and execution time by an order of magnitude.
The solution to this problem is to rewrite the query so that the function is used, not on
the column, but on the value to which we're comparing the column values. To see this
in action, let's set up a test table, an index and 1 million rows of test data, as shown in
Listing 11-3.
CREATE TABLE TestTable
(
ID INT IDENTITY(1, 1)
PRIMARY KEY, – – also creates a Clustered Index
MyDate DATETIME
)
GO
CREATE NONCLUSTERED INDEX NCI_TestTable_MyDate
ON TestTable(MyDate)
- – insert some test data
INSERT INTO TestTable(MyDate)
SELECT TOP 1000000
– – insert million rows going back in time from now
– – at one minute intervals.
DATEADD(n, – ROW_NUMBER()
OVER ( ORDER BY t1.number ),
GETDATE())
FROM master..spt_values t1
CROSS JOIN master..spt_values t2
GO
Listing 11-3: A test table, with index and some test data.
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