SQL Counts with >=1 etc.. Help interpret

[Kristen]

@SQL_learner

My biggest lag here is the use of counts in the subqueries with something like 1<= (select count etc..)

Answered in your previous post:

Need help understanding this SQL

I'm sure Scott was in a rush and meant to suggest something like: AND NOT EXISTS(SELECT 1 FROM TEST t1 WHERE t1.SAMPLE_NUMBER = t.SAMPLE_NUMBER) If you include COUNT(*) in a sub-select SQL will actually go to the trouble of counting up all the rows ... and if you then don't USE that COUNT(*) value somewhere it was a waste of time. EXISTS or NOT EXISTS just needs to establish if there is a single row that matches (and not worry if there is more than one row). If there is a suitable index avai…

Please reply, in that thread, with a question as to what you didn't understand in the answer