oracle wmsys.wm_concat函数

wmsys.wm_concat函数，oracle 10g引入的；

作用：连接字符串，也可以用于将多行数据，转换为一行。

1.用于行列转换

SQL> select * from a;
     ITEMID                    TYPEID TYPENAME
----------- ------------------------- ----------
          1                         2 bbb
          2                         3 ccc
          2                         5 ddd
          3                         5 ddd
          1                         1 aaa
SQL> select * from b;
              ITEMID ITEMNAME
-------------------- ---------
                   1 kkk
                   2 lll
                   3 ooo
SQL> select a.itemid,b.itemname,wmsys.wm_concat(a.typename)
  2  from a,b
  3  where a.itemid=b.itemid
  4  group by a.itemid,b.itemname;
            ITEMID ITEMNAME   WMSYS.WM_CONCAT(A.TYPENAME)
------------------ ---------- -------------------------------
                 1 kkk        bbb,aaa
                 2 lll        ccc,ddd
                 3 ooo        ddd

2.下面将emp表中所有员工姓名连接起来：

SQL> select wmsys.wm_concat(ename) from emp;
WMSYS.WM_CONCAT(ENAME)
--------------------------------------------------------------------------------
SMITH,ALLEN,WARD,JONES,MARTIN,BLAKE,CLARK,SCOTT,KING,TURNER,ADAMS,JAMES,FORD,MIL

那如果我们要将上面一行中员工的姓名区分开来，每个名字显示在一行怎么实现呢？

这要用到正则表达式函数regexp_substr();

SQL> select regexp_substr('SMITH,ALLEN,WARD,JONES,MARTIN,BLAKE,CLARK,SCOTT,KING,TURNER,ADAMS,JAMES,FORD,MIL','[^,]+',1,level)
  2         as cl1
  3  from dual
  4  connect by
  5          level<=length('SMITH,ALLEN,WARD,JONES,MARTIN,BLAKE,CLARK,SCOTT,KING,TURNER,ADAMS,JAMES,FORD,MIL')-
  6          length(replace('SMITH,ALLEN,WARD,JONES,MARTIN,BLAKE,CLARK,SCOTT,KING,TURNER,ADAMS,JAMES,FORD,MIL',',',''))+1;
CL1
--------------------------------------------------------------------------------
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING
TURNER
ADAMS
JAMES
FORD
MIL

--the end--