Daniel Morgan schrieb:
> FlameDance wrote:
>
>> 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
>
>
> SELECT COUNT(*)
> FROM (
> SELECT DISTINCT column1, column2, column3, column4
> FROM mytable);
Daniel, thanks for the suggestion but I am looking for 4 values - your
suggestion gives me 1 value, answering a completely different question.
Stephan
Received on Thu Jun 24 2004 - 01:10:59 CDT
