count distinct

Hi everyone,

I need to know the number of distinct values of 4 columns of the same table. For one column I'd use this statement:

select count (*) from (select distinct column1 from mytable);

This requires a full table scan. For 4 columns I could issue this command 4 times, using a different column each time. That would amount to 4 time consuming full table scans.

select count (*) from (select distinct column1 from mytable);
select count (*) from (select distinct column2 from mytable);
select count (*) from (select distinct column3 from mytable);
select count (*) from (select distinct column4 from mytable);

Is there a way to do this faster, ideally with just one full table scan?

Stephan Received on Wed Jun 23 2004 - 17:04:27 CDT