vb net 2d barcode generator Inside Microsoft SQL Server 2008: T-SQL Programming in .NET

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Inside Microsoft SQL Server 2008: T-SQL Programming
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FiguRe 9-3 Execution plans for inline UDF, Query 1 and Query 2
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FiguRe 9-4 Execution plans for inline UDF, Query 3 and Query 4
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Be aware, though, that if you invoke the inline function from a stored procedure and pass the function the stored procedure s parameters as inputs, you re back to square one in terms of the performance problem . After expansion of the function, the query will still contain references to parameters, and the optimizer will try to come up with a plan that would work for any input . To test this approach, alter the procedure to invoke the function:
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ALTER PROC dbo.GetOrders @orderid AS INT @custid AS INT @empid AS INT @orderdate AS DATETIME = = = = NULL, NULL, NULL, NULL
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9 Dynamic SQL
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WITH RECOMPILE AS SELECT * FROM dbo.fn_GetOrders(@orderid, @custid , @empid, @orderdate); GO
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Run the code provided earlier to test the procedure . You will get the same inefficient plans that where shown earlier in Figure 9-1 .
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Static Solution Based on Multiple Procedures
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There is another static solution that is probably rather obvious, but I will mention it here for the sake of completeness . You could, of course, create a separate procedure for each possible combination of parameters, like so:
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IF OBJECT_ID('dbo.GetOrders0', 'P') IS NOT NULL DROP PROC dbo.GetOrders0; IF OBJECT_ID('dbo.GetOrders1', 'P') IS NOT NULL DROP PROC dbo.GetOrders1; IF OBJECT_ID('dbo.GetOrders2', 'P') IS NOT NULL DROP PROC dbo.GetOrders2; /* ... other procedures ... */ IF OBJECT_ID('dbo.GetOrders15', 'P') IS NOT NULL DROP PROC dbo.GetOrders15; GO CREATE PROC dbo.GetOrders0 AS SELECT orderid, custid, empid, orderdate, filler FROM dbo.Orders; GO CREATE PROC dbo.GetOrders1 @orderdate AS DATETIME AS SELECT orderid, custid, empid, orderdate, filler FROM dbo.Orders WHERE orderdate = @orderdate; GO CREATE PROC dbo.GetOrders2 @empid AS INT AS SELECT orderid, custid, empid, orderdate, filler FROM dbo.Orders WHERE empid = @empid; GO /* ... other procedures ... */ CREATE PROC dbo.GetOrders15 @orderid AS INT, @custid AS INT, @empid AS INT, @orderdate AS DATETIME AS SELECT orderid, custid, empid, orderdate, filler
Inside Microsoft SQL Server 2008: T-SQL Programming
FROM dbo.Orders WHERE orderid AND custid AND empid AND orderdate GO = = = = @orderid @custid @empid @orderdate;
The original GetOrders procedure serves as nothing more than a redirector to the correct procedure based on the input, like so:
ALTER PROC dbo.GetOrders @orderid AS INT @custid AS INT @empid AS INT @orderdate AS DATETIME AS IF @orderid AND @custid AND @empid AND @orderdate IS IS IS IS = = = = NULL, NULL, NULL, NULL
NULL NULL NULL NULL
EXEC dbo.GetOrders0; ELSE IF @orderid IS NULL AND @custid IS NULL AND @empid IS NULL AND @orderdate IS NOT NULL EXEC dbo.GetOrders1 @orderdate = @orderdate; ELSE IF @orderid IS AND @custid IS AND @empid IS NOT AND @orderdate IS EXEC dbo.GetOrders2 @empid = @empid; NULL NULL NULL NULL
/* ... other procedures ... */ ELSE IF @orderid IS NOT NULL AND @custid IS NOT NULL AND @empid IS NOT NULL AND @orderdate IS NOT NULL EXEC dbo.GetOrders15 @orderid = @orderid, @custid = @custid, @empid = @empid, @orderdate = @orderdate; GO
Naturally you will get beautiful plans, because each procedure has only the relevant part in the filter . Subsequent invocations of each procedure can also reuse a previously cached plan . So in terms of performance, this solution is pretty good . Because the solution relies on static code, there s no exposure to SQL injection . However, this solution is a nightmare in terms of maintenance .
9 Dynamic SQL
Solution Based on Dynamic SQL
By using dynamic SQL, you address two problems . First, you get efficient plans . Second, the dynamic batch can reuse execution plans when given the same combination of arguments . Also, by using input parameters in the dynamic batch, you can completely eliminate the exposure to SQL injection . The following code shows a stored procedure implementation that uses dynamic SQL:
ALTER PROC dbo.GetOrders @orderid AS INT @custid AS INT @empid AS INT @orderdate AS DATETIME AS = = = = NULL, NULL, NULL, NULL
DECLARE @sql AS NVARCHAR(1000); SET @sql = N'SELECT orderid, custid, empid, orderdate, filler' + N' /* 27702431-107C-478C-8157-6DFCECC148DD */' + N' FROM dbo.Orders' + N' WHERE 1 = 1' + CASE WHEN @orderid IS NOT NULL THEN N' AND orderid = @oid' ELSE N'' END + CASE WHEN @custid IS NOT NULL THEN N' AND custid = @cid' ELSE N'' END + CASE WHEN @empid IS NOT NULL THEN N' AND empid = @eid' ELSE N'' END + CASE WHEN @orderdate IS NOT NULL THEN N' AND orderdate = @dt' ELSE N'' END; EXEC sp_executesql @stmt = @sql, @params = N'@oid AS INT, @cid AS INT, @eid AS INT, @dt AS DATETIME', @oid = @orderid, @cid = @custid, @eid = @empid, @dt = @orderdate; GO
You can see that an expression involving a filter on a certain column is concatenated only if a value was specified in the corresponding parameter . The expression 1=1 prevents you from needing to determine dynamically whether to specify a WHERE clause at all when no input is specified . This expression has no effect on performance because the optimizer realizes that it always evaluates to TRUE and is therefore neutral . Notice that the procedure was not created with the RECOMPILE option . It s not needed here because the dynamic batch will naturally reuse a plan when given the same list of arguments . It does this because the query string that will be constructed is the same . You can easily observe the efficient plan reuse here by querying sys.syscacheobjects .
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