Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

-- This won’t work
DECLARE @NumberOfLetters int = 15;
EXEC(‘SELECT LEFT(Name,’ + CAST(@NumberOfLetters AS varchar) + ‘) AS ShortName
FROM Production.Product’);
GO
-- But this does
DECLARE @NumberOfLetters AS int = 15;
DECLARE @str AS varchar(255);
SET @str = ‘SELECT LEFT(Name,’ + CAST(@NumberOfLetters AS varchar) + ‘) AS ShortName
FROM Production.Product’;
EXEC(@str);
The first instance gets an error message because the CAST function needs to be fully resolved prior to the
EXEC line:
Msg 102, Level 15, State 1, Line 9
Incorrect syntax near ‘CAST’.
But the second line works just fine because it is already a complete string:
ShortName
---------------
Adjustable Race
All-Purpose Bik
AWC Logo Cap
...
...
Women’s Tights,
Women’s Tights,
Women’s Tights,
EXEC and UDFs
This is a tough one to touch on because we haven’t gotten to user-defined functions as yet, but suffice to
say that you are not allowed to use EXEC to run dynamic SQL within a UDF — period. (EXEC to run a
sproc is, however, legal in a few cases.)
Control-of-Flow Statements
Control-of-flow statements are a veritable must for any programming language these days. I can’t imagine
having to write my code where I couldn’t change what commands to run depending on a condition.
T-SQL offers most of the classic choices for control of flow situations, including:
❑ IF ... ELSE
❑ GOTO
❑ WHILE
❑ WAITFOR
❑ TRY/CATCH
Chapter 11: Writing Scripts and Batches
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