SQL SERVER – Stream Aggregate Showplan Operator – Reason of Compute Scalar before Stream Aggregate February 5, 2010 by pinaldave | Edit I keep a check on the questions received from my readers; when any question crosses my threshold, I surely try to blog about it online. Stream Aggregate is a quite commonly encountered showplan operator. I have often found it in very simple COUNT(*) operation’s execution plan. If you like to read an official note on the subject, you can read the same on Book Online over here. The Stream Aggregate operator groups rows by one or more columns and then calculates one or more aggregate expressions returned by the query. Click more for further story.