Hugo Kornelis (8/26/2010)

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and


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 int;
  SELECT @b;
  GOTO Label3;
Label2:
  SET @b = 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)