Convert columns to rows in SQL [duplicate]

问题

I need to write a query which takes rows and converts it into columns - here's my table:

Count    fname   lname   id
-----------------------------
1        abc     def    20
2        pqr            20      
3        abc     xyz    20  
4        xyz     xyz    20
1        abc     def    21
1        pqr     xyz    22
2        abc     abc    22

This is the output I'm trying to produce:

id  fname  lname  fname  lname  fname  lname  fname  lname
-------------------------------------------------------------
20  abc    def    pqr    NULL   abc    xyz    xyz    xyz
21  abc    def    NULL   NULL   NULL   NULL   NULL   NULL   
22  abc    abc    NULL   NULL   NULL   NULL   NULL   NULL

The max value of count for each id is 4. I'm using Oracle 9i.

回答1:

Here's another one you might have some luck with. I like @ThinkJet's but not sure how much decode costs (if more or less than this below.

SELECT
   T1.ID,
   T1.fname,
   T1.lname,
   T2.fname,
   T2.lname,
   T3.fname,
   T3.lname,
   T4.fname,
   T4.lname
FROM
      table T1
   LEFT JOIN
      table T2
   ON
         T1.ID = T2.ID
      AND T2.count = 2
   LEFT JOIN
      table T3
   ON
         T1.ID = T3.ID
      AND T3.count = 3
   LEFT JOIN
      table T4
   ON
         T1.ID = T4.ID
      AND T4.count = 4
WHERE
   T1.count = 1

回答2:

Look at this example, same principle as in @Mike M. answer, but with true Oracle realization:

  create table my_table (
    id    number,
    fname varchar2(255),
    lname varchar2(255),
    cnt   number
  );

  insert into my_table(cnt, fname, lname, id) values(1,'abc','def',20);
  insert into my_table(cnt, fname, lname, id) values(2,'pqr',''   ,20);      
  insert into my_table(cnt, fname, lname, id) values(3,'abc','xyz',20);  
  insert into my_table(cnt, fname, lname, id) values(4,'xyz','xyz',20);
  insert into my_table(cnt, fname, lname, id) values(1,'abc','def',21);
  insert into my_table(cnt, fname, lname, id) values(1,'pqr','xyz',22);
  insert into my_table(cnt, fname, lname, id) values(2,'abc','abc',22);

  select 
    tbl.id,
    min(decode(tbl.cnt, 1 , fname, null)) fname_1,
    min(decode(tbl.cnt, 1 , lname, null)) lname_1,
    min(decode(tbl.cnt, 2 , fname, null)) fname_2,
    min(decode(tbl.cnt, 2 , lname, null)) lname_2,
    min(decode(tbl.cnt, 3 , fname, null)) fname_3,
    min(decode(tbl.cnt, 3 , lname, null)) lname_3,
    min(decode(tbl.cnt, 4 , fname, null)) fname_4,
    min(decode(tbl.cnt, 4 , lname, null)) lname_4
  from 
    my_table tbl
  group by 
    tbl.id 
  order by 
    tbl.id  
  ;

回答3:

I know you're after an Oracle 9i solution, but Oracle 11 introduces PIVOT, which allows you to do queries like:

select *
  from mb_test
 pivot ( max(fname ) as fname,
         max(lname) as lname
   for count in (1,2,3,4)
       )
order by id
;

which gives:

 ID  1_fname  1_lname  2_fname  2_lname  3_fname  3_lname  4_fname  4_lname
20  abc      def      pqr      null     abc      xyz      xyz      xyz
21  abc      def      null     null     null     null     null     null
22  pqr      xyz      abc      abc      null     null     null     null

Not quite what you were after, but extremely useful in many circumstances.... and almost worth the upgrade for PIVOT and UNPIVOT alone

EDIT

Modified to put fname and lname in separate columns