SQL Server 2005 recursive query with loops in data - is it possible?

Question

I\'ve got a standard boss/subordinate employee table. I need to select a boss (specified by ID) and all his subordinates (and their subrodinates, etc). Unfortunately the rea

Answer 1

You don't have to do it recursively. It can be done in a WHILE loop. I guarantee it will be quicker: well it has been for me every time I've done timings on the two techniques. This sounds inefficient but it isn't since the number of loops is the recursion level. At each iteration you can check for looping and correct where it happens. You can also put a constraint on the temporary table to fire an error if looping occurs, though you seem to prefer something that deals with looping more elegantly. You can also trigger an error when the while loop iterates over a certain number of levels (to catch an undetected loop? - oh boy, it sometimes happens.

The trick is to insert repeatedly into a temporary table (which is primed with the root entries), including a column with the current iteration number, and doing an inner join between the most recent results in the temporary table and the child entries in the original table. Just break out of the loop when @@rowcount=0! Simple eh?