oracle 列转行sql详解
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--当期时间贷款时间
SELECT DK_ID, max(substr(activeDate, 2)) activeDate
FROM (SELECT DK_ID, sys_connect_by_path(activeDate, ',') activeDate
FROM (SELECT DK_ID,
activeDate,
DK_ID || rn rchild,
DK_ID || (rn - 1) rfather
FROM (SELECT TEMP.DK_ID,
--查询项目所在地树形结构全名
SELECT t.area_id,
substr(sys_connect_by_path(t.area_name, '-'), 2) as allname ,
connect_by_root t.area_name as root, --是单一操作符,返回当前层的最顶层节点connect_by_isleaf as IsLeaf, --是伪列,判断当前层是否为叶子节点,1代表是,0代表否
level as lel --是伪列,显示当前节点层所处的层数
FROM dk_project_area_info t
START WITH t.area_name = '项目所在地'
CONNECT BY PRIOR t.area_id = t.area_pid
SYS_CONNECT_BY_PATH 学习2008-09-08 10:59SELECT ename
FROM scott.emp
START WITH ename = 'KING'
CONNECT BY PRIOR empno = mgr;
得到结果为:KING
JONES
SCOTT
ADAMS
FORD
SMITH
BLAKE
ALLEN
WARD
MARTIN
TURNER
JAMES
而:SELECT SYS_CONNECT_BY_PATH(ename, '>') "Path"
FROM scott.emp
START WITH ename = 'KING'
CONNECT BY PRIOR empno = mgr;
得到结果为:>KING
>KING>JONES
>KING>JONES>SCOTT
>KING>JONES>SCOTT>ADAMS
>KING>JONES>FORD
>KING>JONES>FORD>SMITH
>KING>BLAKE
>KING>BLAKE>ALLEN
>KING>BLAKE>WARD
>KING>BLAKE>MARTIN
>KING>BLAKE>TURNER
>KING>BLAKE>JAMES
>KING>CLARK
>KING>CLARK>MILLER
其实SYS_CONNECT_BY_PATH这个函数是oracle9i才新提出来的!
它一定要和connect by子句合用!
第一个参数是形成树形式的字段,第二个参数是父级和其子级分隔显示用的分隔符!
START WITH 代表你要开始遍历的的节点,
CONNECT BY PRIOR 是标示父子关系的对应!
如下例子:select max(
substr(
sys_connect_by_path(column_name,',')
,2)
)
from (select column_name,rownum rn from user_tab_columns where table_name ='AA_TEST')
start with rn=1 connect by rn=rownum ;
是将列用,进行分割成为一行,然后将首个,去掉,只取取最大的那个数据。
---------
下面是别人的例子:
1、带层次关系
SQL> create table dept(deptno number,deptname varchar2(20),mgrno number);
Table created.
SQL> insert into dept values(1,'总公司',null);
1 row created.
SQL> insert into dept values(2,'浙江分公司',1);
1 row created.
SQL> insert into dept values(3,'杭州分公司',2);
1 row created.
SQL> commit;
Commit complete.
SQL> select max(substr(sys_connect_by_path(deptname,','),2)) from dept connect by prior deptno=mgrno;
MAX(SUBSTR(SYS_CONNECT_BY_PATH(DEPTNAME,','),2))
-------------------------------------------------------------------------------- 总公司,浙江分公司,杭州分公司
2、行列转换
如把一个表的所有列连成一行,用逗号分隔:
SQL> select max(substr(sys_connect_by_path(column_name,','),2))
from (select column_name,rownum rn from user_tab_columns where table_name ='DEPT') start with rn=1 connect by rn=rownum ;
MAX(SUBSTR(SYS_CONNECT_BY_PATH(COLUMN_NAME,','),2))
-------------------------------------------------------------------------------- DEPTNO,DEPTNAME,MGRNO