How to select the first record?

Question

Hi,
Could anyone tell me how to select the first record of every
group?
ex, I want to find out every customer their first purcaseDate.
CustomerID PurcaseDate Region
A00000001 2001/01/01 AA
A00000001 2001/02/02 AA
A00000002 2001/03/01 AC
A00000002 2001/05/07 AC
A00000003 2001/03/05 DD
result:
A00000001 2001/01/01 AA
A00000002 2001/03/01 AC
A00000003 2001/03/05 DD
Thanks

Answer 1

Vincent,
You could do it as Carl suggested, with a couple of
corrections.  You would need to include the CustomNo column in
the order by clause of your cursor.  You would also need to add
a where clause to your update statement, otherwise everywhere
Region in the table would be updated with the same value of the
last CustomNo in the cursor, regardless of the CustomNo in the
table.  See corrected code below:
DECLARE
  CURSOR     cust
  IS
  SELECT     DISTINCT CustomNo, Region, Purchase_Date
  FROM       my_table
  ORDER BY   CustomNo, Purchase_Date, Region;
  c_customer VARCHAR2 (9) := '...';
  c_region   VARCHAR2 (2) := '..';
  cntr       NUMBER := 0;
BEGIN
  FOR x IN cust
  LOOP
    IF x.CustomNo != c_customer
    THEN
      c_customer := x.CustomNo;
      c_region := x.Region;
    ELSE
      UPDATE my_table
      SET    Region = c_region
      WHERE  CustomNo = c_customer;
      cntr := cntr + 1;
      IF cntr = 25
      THEN
        COMMIT;
        cntr := 0;
      END IF;
    END IF;
  END LOOP;
  COMMIT;
EXCEPTION
  WHEN OTHERS THEN 
    NULL;
END;
Another option is that you could just use one update statement,
like this:
UPDATE my_table a
SET    Region =
       (SELECT DISTINCT Region
        FROM   my_table b
        WHERE  (CustomNo, Purchase_Date) IN
               (SELECT   CustomNo, MIN (Purchase_Date)
                FROM     my_table
                GROUP BY CustomNo)
        AND    a.CustomNo = b.CustomNo)
Barbara