Hugo Kornelis (8/26/2010)

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da-zero (8/26/2010)

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I do not really understand how the scope of the type variable works. It seems you can define it over and over again, without an error being thrown?

and

martin.whitton (8/26/2010)

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It's interesting that a variable can be declared multiple times if it's within a "while" loop (provided that it's only declared once in each iteration).

When I first read the question I thought that declaring @a within the loop would cause an error on the second iteration.

The variable is actually declared once. Declarations are not relly executable statements. They are processed when a batch is parsed, not when it it executed. The declaration has to be positioned before the use in "left to right / top to bottom" order, not in execution order. That is why this works, even though the code path that containst the declaration is never executed.

IF 1 = 2

BEGIN;

PRINT 'Skip this';

DECLARE @a int;

END;

ELSE

BEGIN;

SET @a = 1;

END;

SELECT @a;

And this works as well, even though the part where the declaration sits is executed AFTER the assignment:

GOTO Label2;

Label1:

DECLARE @b-2 int;

SELECT @b-2;

GOTO Label3;

Label2:

SET @b-2 = 3;

GOTO Label1;

Label3:

go

(Note that I do not endorse using GOTO in T-SQL code, nor deliberately writing spaghetti code for any other purposes than illustrating the difference between order of parsing and order of execution)