Query help in select Distinct on one column.

Question

CREATE GLOBAL TEMPORARY TABLE Table1 (
ID1 varchar2(100) ,
Name1 varchar2(100),
Name11 varchar2(100)
insert into Table1 values ('a','n1','h3');
insert into Table1 values('b','n2','h2');
insert into Table1 values('a','n3','h1');
insert into Table1 values('c','n4','h5');
insert into Table1 values ('c','n5','h4');
insert into Table1 values('d','n6','h6');
select * from Table1;
ID1,NAME1,     NAME11
a,     n1,     h3
b,     n2,     h2
a,     n3,     h1
c,     n4,     h5
c,     n5,     h4
d,     n6,     h6
I am trying to select distinct ID1 and all values associated with it which is max row.I want to result as -
ID1,NAME1,     NAME11
a,     n3,     h1
b,     n2,     h2
c,     n5,     h4
d,     n6,     h6
Can you please help me to write simple query to get above result.
Edited by: 871447 on Jul 25, 2011 9:42 AM
Edited by: 871447 on Jul 25, 2011 9:45 AM

Answer 1

Hi,
Do a self-join, to combine the two rows for each value of id1 onto one output row.
Make it an outer join, in case there is only one row with a vlaue for id1.
SELECT  l.id1
,     l.name1
,     NVL ( r.name11
         , l.name11
         )          AS name11
FROM              table1     l
LEFT OUTER JOIN     table1     r  ON  l.id1     = r.id1
                          AND l.name1     < r.name1
;Edited by: Frank Kulash on Jul 25, 2011 12:57 PM
Sorry, I mis-read the problem.
Lee's solution, above, assumes that name1 is unique, as it is in your sample data.
What output would you want if that's not the case?
If name1 is not unique, but the combination of (id1, name1) is unique, then you can modify Lee's solution like this:
SELECT  *
FROM    table1
WHERE   (id1, name1) IN (
                    SELECT    id1
                    ,       MAX (name1)
                           FROM          table1
                    GROUP BY  id1
;Or, if you can't make any assumptions about uniqueness, you might need something like this:
WITH     got_r_num     AS
     SELECT  id1, name1, name11
     ,     ROW_NUMBER () OVER ( PARTITION BY  id1
                               ORDER BY          name1     DESC
                         ,                name11     DESC
                       )      AS r_num
     FROM     table1
SELECT  id1, name1, name11
FROM     got_r_num
WHERE     r_num     = 1
;