多行数据合并成一条数据的最简单方法。

使用Oracle数据库自带的函数：wmsys.wm_concat可以解决此问题。

example:select wmsys.wm_concat(t.username) from student t

 

SQL> select version from v$instance;
 
VERSION
-----------------
10.2.0.1.0
 
SQL>
SQL> create table IDTABLE
  2  (
  3    id  number,
  4    val varchar2(20)
  5  )
  6  ;
 
Table created
 
SQL>
SQL> insert into IDTABLE (ID, VAL)
  2  values (10, 'abc');
 
1 row inserted
SQL> insert into IDTABLE (ID, VAL)
  2  values (10, 'abc');
 
1 row inserted
SQL> insert into IDTABLE (ID, VAL)
  2  values (10, 'def');
 
1 row inserted
SQL> insert into IDTABLE (ID, VAL)
  2  values (10, 'def');
 
1 row inserted
SQL> insert into IDTABLE (ID, VAL)
  2  values (20, 'ghi');
 
1 row inserted
SQL> insert into IDTABLE (ID, VAL)
  2  values (20, 'jkl');
 
1 row inserted
SQL> insert into IDTABLE (ID, VAL)
  2  values (20, 'mno');
 
1 row inserted
SQL> insert into IDTABLE (ID, VAL)
  2  values (20, 'mno');
 
1 row inserted
 
SQL> select id,val from idtable;
 
        ID VAL
---------- --------------------
        10 abc
        10 abc
        10 def
        10 def
        20 ghi
        20 jkl
        20 mno
        20 mno
 
8 rows selected
 
SQL> commit;
 
Commit complete
 
SQL>
SQL> SELECT ID, WMSYS.WM_CONCAT(VAL) AS ENAMES
  2    FROM IDTABLE
  3   GROUP BY ID;
 
        ID ENAMES
---------- --------------------------------------------------------------------------------
        10 abc,abc,def,def
        20 ghi,jkl,mno,mno
 
SQL>
SQL> SELECT ID, WMSYS.WM_CONCAT(DISTINCT VAL) AS ENAMES
  2    FROM IDTABLE
  3   GROUP BY ID
  4   ORDER BY ID;
 
        ID ENAMES
---------- --------------------------------------------------------------------------------
        10 abc,def
        20 ghi,jkl,mno
 
SQL>
SQL> SELECT ID, VAL, WMSYS.WM_CONCAT(VAL) OVER(PARTITION BY ID) AS ENAMES
  2    FROM IDTABLE
  3   ORDER BY ID;
 
        ID VAL               ENAMES
---------- -------------------- --------------------------------------------------------------------------------
        10 abc                abc,abc,def,def
        10 abc                abc,abc,def,def
        10 def                abc,abc,def,def
        10 def                abc,abc,def,def
        20 ghi                ghi,jkl,mno,mno
        20 jkl                 ghi,jkl,mno,mno
        20 mno               ghi,jkl,mno,mno
        20 mno               ghi,jkl,mno,mno
 
8 rows selected
 
SQL>
SQL> SELECT ID, VAL, WMSYS.WM_CONCAT(VAL) OVER(ORDER BY ID, VAL) AS ENAMES
  2    FROM IDTABLE
  3   ORDER BY ID;
 
        ID VAL               ENAMES
---------- -------------------- --------------------------------------------------------------------------------
        10 abc                abc,abc
        10 abc                abc,abc
        10 def                abc,abc,def,def
        10 def                abc,abc,def,def
        20 ghi                abc,abc,def,def,ghi
        20 jkl                 abc,abc,def,def,ghi,jkl
        20 mno               abc,abc,def,def,ghi,jkl,mno,mno
        20 mno               abc,abc,def,def,ghi,jkl,mno,mno
 
8 rows selected