In SQL Server 2008 its possible to debug queries in SQL Server Management Studio. It is very simple and easy.
In toolbar we have toolbar of Debug , if not we can open it as below
Now we will run below query in SQL Server Management Studio
DECLARE @I INT
SET @I = 1
WHILE @I <= 100
SET @I = @I + 1
Now start debugging as shown below
Open watch window as show below
Now create breakpoints in the query, by clicking at starting of the row.
Type Parameter @i in the Name field of watch window. Monitor the value of @i in the watch window.
Now I want to set its value to some new number.
See below how to modify it. Modify it and start debugging.