COUNT(DISTINCT) on multiple columns?

Question

Is there an easier way of doing a COUNT(DISTINCT...) on multiple items than converting them to strings and concatenating them?
i.e. if I have a table with column string1 as VARCHAR2(1000), number2 as NUMBER, and date3 as DATE, and I want a count on how many distinct combinations of the three exist, is there a better way than:
SELECT COUNT(DISTINCT string1 || TO_CHAR(number2) || TO_CHAR(date3, 'YYYYMMDD'))-- Don

Answer 1

Hi,
Why not a group by?
SQL> ed
Wrote file afiedt.buf
  1  with t as
  2  (
  3  select 'string1' string1, 1 number1, to_date('10-NOV-2009','DD-MON-YYYY') date1 from dual
  4  union all select 'string2',1,to_date('10-NOV-2009','DD-MON-YYYY') from dual
  5  union all select 'string1',1,to_date('11-NOV-2009','DD-MON-YYYY') from dual
  6  union all select 'string1',2,to_date('11-NOV-2009','DD-MON-YYYY') from dual
  7  union all select 'string2',1,to_date('10-NOV-2009','DD-MON-YYYY') from dual
  8  )
  9  select string1, number1, date1 from t
10* group by string1, number1, date1
SQL> /
STRING1    NUMBER1 DATE1
string1          1 11-NOV-09
string2          1 10-NOV-09
string1          1 10-NOV-09
string1          2 11-NOV-09
SQL> ed
Wrote file afiedt.buf
  1  with t as
  2  (
  3  select 'string1' string1, 1 number1, to_date('10-NOV-2009','DD-MON-YYYY') date1 from dual
  4  union all select 'string2',1,to_date('10-NOV-2009','DD-MON-YYYY') from dual
  5  union all select 'string1',1,to_date('11-NOV-2009','DD-MON-YYYY') from dual
  6  union all select 'string1',2,to_date('11-NOV-2009','DD-MON-YYYY') from dual
  7  union all select 'string2',1,to_date('10-NOV-2009','DD-MON-YYYY') from dual
  8  )
  9  select string1, number1, date1 from t
10  group by string1, number1, date1
11* having count(*) > 1
SQL> /
STRING1    NUMBER1 DATE1
string2          1 10-NOV-09-Arun