Question

What I want to do is add a COUNT into a query that is joined on several tables, but I only want to count the thing if it meets a specific condition.

I want the count to only count the rows that have a ReceivedDate like so:

COUNT(ReceivedDate = "0000-00-00 00:00:00", plpq.PurchaseOrderID) AS OrdersForPart

Is there any way to achieve this without having to resort to a sub-query?

Answer 1

Assuming you might want to perform some aggregation on the other rows and thus can’t just exclude them entirely in the WHERE clause.

COUNT(CASE 
        WHEN ReceivedDate = "0000-00-00 00:00:00" 
        THEN plpq.PurchaseOrderID 
      END) AS OrdersForPart

If this isn’t the case the WHERE clause is of course the best option.