Execute Dynamic SQL commands in SQL Server

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In some applications having hard-coded SQL statements is not appealing, because of the dynamic nature of the queries being issued against the database server. Because of this sometimes there is a need to dynamically create a SQL statement on the fly and then run that command. This can be done quite simply from the application perspective where the statement is built on the fly whether you are using ASP.NET , ColdFusion or any other programming language. But how do you do this from within a SQL Server stored procedure? SQL Server offers a few ways of running a dynamically built SQL statement. These ways are: Writing a query with parameters Using EXEC Using sp_executesql Writing a query with parameters This first approach is pretty straightforward if you only need to pass parameters into the WHERE clause of your SQL statement. Let’s say we need to find all records from the Customers table where City = ‘London’. This can be done easily as the following example shows.
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The COALESCE Function

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A more efficient approach to creating dynamic WHERE clauses involves using the COALESCE function. This function returns the first non-null expression in its expression list. The following example shows how it works. 

DECLARE @Exp1 varchar(30),
       @Exp2 varchar(30)

SET @Exp1 = NULL
SET @Exp2 = 'SQL Server'

SELECT COALESCE(@Exp1,@Exp2)

--Results--

------------------------------
SQL Server

The function processes the expression list from left-to-right and returns the first non-null value. The COALESCE function can process an infinite number of expressions (e.g., COALESCE(@Exp1,@Exp2,@Exp3,@Exp4,...)), but for the example presented in this article only two are needed.

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Unknown said…
Hello
Earlier i am bit confused on COALESCE function,Now i am very clear with COALESCE functio.

Nice artilce.
Thanks Guy's
September 22, 2009 at 3:19 AM
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