Listing 1: Analyzing a T-SQL Query from the Inside Out
DECLARE @customerid int
SET @customerid=3
[BEGIN CALLOUT A]
SELECT e.cname, f.value AS value  -- Get the value for each cname and max tid.
  FROM [BEGIN CALLOUT B] (SELECT d.cname, max(d.tid) AS tid 
                   -- Get the max tid for every cid
          FROM [BEGIN CALLOUT C] (SELECT a.cname, b.pid, max(c.tid) AS tid 
                   -- Get the max tid for every cid and pid.
                  FROM dbo.cats AS a
                    INNER JOIN dbo.prods AS b
                      ON (a.cid=b.cid)
                    LEFT OUTER JOIN dbo.trans AS c
                      ON (b.pid=c.pid AND c.custid = @customerid)
                  GROUP BY a.cname, b.pid) AS d
[END CALLOUT C]          GROUP BY d.cname) AS e
[END CALLOUT B]
  LEFT OUTER JOIN dbo.trans AS f
    ON (f.tid=e.tid)
[END CALLOUT A]