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Find the count of members who have made at least one booking

Question

Find the total number of members (including guests) who have made at least one booking.
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Expected Results

count
30

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select count(distinct memid) from cd.bookings          

          

            


Your first instinct may be to go for a subquery here.  Something like the below:



select count(*) from 
	(select distinct memid from cd.bookings) as mems



This does work perfectly well, but we can simplify a touch with the help of a little extra knowledge in the form of COUNT DISTINCT.  This does what you might expect, counting the distinct values in the passed column.
            

          

        

      

      
      

        
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Take a look at COUNT DISTINCT
      

      

        

	  
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