11-26-2013 01:11 PM
select a.*, b.* from a left join b on a.key=b.key I want all a rows and matched b rows, but not including those b rows with empty key. Q1: if a.key=missing and b.key=missing then they will be matched. How to avoid that? Q2: if I add "where b.key is not missing", all rows with a.key=missing will be removed. So, WHERE is applied after Left Join? Any efficient way?
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