SQL Server variable scope in a stored procedure

I would like to declare a variable within an if/else statement in a SQL Server stored procedure. I understand that this is fairly impossible because SQL Server doesn't do memory management wi开发者_Go百科th respect to declaration of variables within procedures. Is there a way to have a variable scoped in an if/else statement, then redeclare a variable with the same name in another if/else statement? For example:

create procedure Foo
as
begin  
    if exists (x)
    begin
        declare @bob int
        set bob = 1
    end
    else
    begin
        declare @bob int
        set bob = 2
    end
end

From books online:

The scope of a variable is the range of Transact-SQL statements that can reference the variable. The scope of a variable lasts from the point it is declared until the end of the batch or stored procedure in which it is declared.

However. Nothing keeps you from doing this:

create procedure Foo as begin

declare @bob int

if exists (x)
begin
    set @bob = 1
end
else
begin
    set @bob = 2
end

end

No, SQL is pretty funny/weird like that

Declare the variable before the if exists block of code

so

declare @bob int 
set @bob = 2 

if exists(x) 
begin   
    set @bob = 1 
end

Now, take a look at these examples and try to guess what happens

WHILE 1 = 2 --not true of course
BEGIN
  DECLARE @VAR INT;
END
SET @VAR = 1;

SELECT @VAR;

This of course works, but it is not initialized every time

DECLARE @loop INT
SET @loop = 0

WHILE @loop <=6
BEGIN
        DECLARE @VAR INT
        SET @VAR = COALESCE(@VAR,0) + 1
        SET @loop = @loop +1
END

SELECT @VAR

is there some reason why you can't do :

declare @bob int 
if exists(x) 
begin   set @bob = 1 end 
else 
begin  set @bob = 2 end 

You could resort to using dynamic SQL:

if exists (x)
begin
    exec sp_executesql N'
        declare @bob int
        set @bob = 1
    ';
end
else
begin
    exec sp_executesql N'
        declare @bob int
        set @bob = 2
    ';
end