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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COALESCE And ISNULL Differences

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Run the following block of code


-- The result is 7, integer math
SELECT 15 / ISNULL(CONVERT(INT,NULL), 2.00)

--The result is 7.5, which is correct
SELECT 15 / COALESCE(CONVERT(INT,NULL), 2.00)

You will see that the result is not the same ISNULL does integer math while COALESCE does not

COALESCE correctly promotes its arguments to the highest data type in the expression list.
ISNULL just looks at the first datatype, which is an integer (15) and makes everything an int
COALESCE looks at 2.00 and 15 and then promotes the integer to decimal

Another example is returning the first non null value, ISNULL can only take 2 values while COALESCE can take a whole lot more
Here we have 4 variables and all except for one are null

DECLARE @Var1 VARCHAR(20)
DECLARE @Var2 VARCHAR(20)
DECLARE @Var3 VARCHAR(20)
DECLARE @Var4 VARCHAR(20)

SELECT @Var4 = 'ABC'


--This will return ABC
SELECT COALESCE(@Var1,@Var2,@Var3,@Var4)

Comments

Unknown said…
good example to understand the differance
November 27, 2010 at 3:10 PM
AnilKumar said…
My Table is Like below
Create table ABC (column nvarchar(2000))

insert ABC values ('ab1|ab2|ab3|ab4|ab5|ab6|ab7|ab8')

here i want only display ab7

ab7
March 15, 2012 at 8:22 PM
Janardhan said…
select SUBSTRING(column1,25,3) from ABC
January 18, 2013 at 1:32 AM
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