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

DECLARE @InVar varchar(50);
DECLARE @OutVar varchar(50);
-- Set up our string to feed into the EXEC command
SET @InVar = ‘SELECT @OutVar = FirstName FROM Person.Contact WHERE ContactID = 1’;
-- Now run it
EXEC (@Invar);
-- Now, just to show there’s no difference, run the select without using a in variable
EXEC (‘SELECT @OutVar = FirstName FROM Person.Contac WHERE ContactID = 1’);
-- @OutVar will still be NULL because we haven’t been able to put anything in it
SELECT @OutVar;
Now, look at the output from this:
Msg 137, Level 15, State 1, Line 1
Must declare the scalar variable “@OutVar”.
Msg 137, Level 15, State 1, Line 1
Must declare the scalar variable “@OutVar”.
--------------------------------------------------
NULL
(1 row(s) affected)
SQL Server wastes no time in telling us that we are scoundrels and clearly don’t know what we’re doing.
Why do we get a Must Declare error message when we have already declared @OutVar? Because we’ve
declared it in the outer scope — not within the EXEC itself.
Let’s look at what happens if we run things a little differently:
USE AdventureWorks2008;
-- This time, we only need one variable. It does need to be longer though.
DECLARE @InVar varchar(200);
/* Set up our string to feed into the EXEC command. This time we’re going
** to feed it several statements at a time. They will all execute as one
** batch.
*/
SET @InVar = ‘DECLARE @OutVar varchar(50);
SELECT @OutVar = FirstName FROM Person.Person WHERE BusinessEntityID = 1;
SELECT ‘’The Value Is ‘’ + @OutVar’;
-- Now run it
EXEC (@Invar);
This time we get back results closer to what we expect:
Chapter 11: Writing Scripts and Batches
---------------------------------------------------------------
The Value Is Ken
Notice the way that I’m using two quote marks right next to each other to indicate that I really want a
quote mark rather than to terminate my string.
So, what we’ve seen here is that we have two different scopes operating, and nary the two shall meet.
There is, unfortunately, no way to pass information between the inside and outside scopes without using
an external mechanism such as a temporary table or a special stored procedure called sp_executesql.
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