Variables scope which are defined within a while block in stored procedures - SQl Server

Question

I\'ve come across a interesting scenario (at least for me) in a stored procedure. Would like to have experts opinion and thoughts on it.

DECLARE @loopcounter         


        

Answer 1

 DECLARE @loopcounter INT
 DECLARE @insidevalue int
   SET @loopcounter=10
       WHILE @loopcounter > 0
        BEGIN
          IF (@loopcounter%2 = 0)
          BEGIN
          SET @insidevalue = @loopcounter
          PRINT 'Value_' + CAST(@insidevalue AS NVARCHAR) + '_'
          END
    ELSE
      PRINT 'Value_'+' '+'_'
      SET @loopcounter = @loopcounter - 1
   END

Answer 2

The variable scope is the whole batch in this case a stored procedure.

It isn't re-declared every loop

So this is exactly as expected

Edit:

There is a recent blog article which is quite similar. The author was quickly corrected :-)

Answer 3

From Declare:

The scope of a local variable is the batch in which it is declared.

There are no more "local" scoping rules in T-SQL. It also means that you can't declare the same variable name inside IF and ELSE blocks.

All Declare does is declare a variable. It has no relation to assignment. The value of any variable that has never been assigned to is NULL. But thereafter, the only way the variables value will become NULL again is through an explicit assignment.

If you need it to be NULL at the top of each loop iteration, therefore, you must explicitly assign it.

Answer 4

Integer data types often don't have NULL's only 0's

Declare statement won't happen each time within the loop

why don't you just use

DECLARE @loopcounter INT
SET @loopcounter=10
WHILE @loopcounter > 0
BEGIN
  IF @loopcounter%2 = 0
  PRINT 'Value_' + CAST(@loopcounter AS NVARCHAR) + '_'
  else
  PRINT 'Value_ _'
  SET @loopcounter = @loopcounter - 1
END

That gives:

Value_10_
Value_ _
Value_8_
Value_ _
Value_6_
Value_ _
Value_4_
Value_ _
Value_2_
Value_ _

Answer 5

In T-SQL a WHILE..END is not individually scoped, you can for example SELECT @insidevalue after the WHILE's END.

Answer 6

From Transact-SQL Variables

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.

The DECLARE is not in itself an executable statement. The variable declarations are all identified at compile time and the memory reserved for them in the execution context.

If you use the 2008+ Declare and Set syntax. The Set part of the statement will occur every loop iteration however.

DECLARE @loopcounter INT
SET @loopcounter=10

WHILE @loopcounter > 0
BEGIN
  DECLARE @insidevalue INT = NULL

  IF (@loopcounter%2 = 0)
  SET @insidevalue = @loopcounter

  PRINT 'Value_' + CAST(@insidevalue AS NVARCHAR) + '_'

  SET @loopcounter = @loopcounter - 1
END