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 bbb2                         3 ccc2                         5 ddd3                         5 ddd1                         1 aaa
SQL> select * from b;ITEMID ITEMNAME
-------------------- ---------1 kkk2 lll3 ooo
SQL> select a.itemid,b.itemname,wmsys.wm_concat(a.typename)2  from a,b3  where a.itemid=b.itemid4  group by a.itemid,b.itemname;ITEMID ITEMNAME   WMSYS.WM_CONCAT(A.TYPENAME)
------------------ ---------- -------------------------------1 kkk        bbb,aaa2 lll        ccc,ddd3 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 cl13  from dual4  connect by5          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

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