I have a very basic LEFT OUTER JOIN to return all results from the left table and some additional information from a much bigger table. The left table contains 4935 records yet when I LEFT OUTER JOIN it to an additional table the record count is significantly larger.
As far as I'm aware it is absolute gospel that a LEFT OUTER JOIN will return all records from the left table with matched records from the right table and null values for any rows which cannot be matched, as such it's my understanding that it should be impossible to return more rows than exist in the left table, but it's happening all the same!
SQL Query follows:
SELECT SUSP.Susp_Visits.SuspReason, SUSP.Susp_Visits.SiteID FROM SUSP.Susp_Visits LEFT OUTER JOIN DATA.Dim_Member ON SUSP.Susp_Visits.MemID = DATA.Dim_Member.MembershipNum
Perhaps I have made a mistake in the syntax or my understanding of LEFT OUTER JOIN is incomplete, hopefully someone can explain how this could be occurring?
Thanks for the great answers, my understanding of LEFT OUTER JOINS is now much better, could anyone however suggest a way this query could be modified so that I only get as many records returned as exist in the left table?
This query is purely to generate a report and the duplicate matches simply confuse matters.