SQL Server如何计算出估计的行数？

I'm trying to debug a fairly complex stored procedure that joins across many tabls (10-11). I'm seeing that for a part of the tree the estimated number of rows drasticly differs from the actual number of rows - at its worst SQL server estimates that 1 row will be returned, when in actuality 55,000 rows are returned!I'm trying to debug a fairly complex stored pro