2个sql 函数dbms_lob.substr 和 wm_concat

Posted 2020-10-14

转自：

http://blog.csdn.net/wenzhongyan/article/details/50315473

http://blog.csdn.net/ojerryzuo/article/details/53927057

 

1、通过dbms_lob.substr（）转换clob字段为varchar2类型

在查询dba_stat_extensions视图的时候，其中extension字段是clob类型，直接通过select语句无法显示，如下：

需要通过dbms_lob.substr（）转换

SELECT owner ,a.table_name,trim(dbms_lob.substr(extension,4000)) as extension  FROM dba_stat_extensions a 转换后显示如下：

 

 

2.

首先让我们来看看这个神奇的函数wm_concat(列名),该函数可以把列值以","号分隔起来,并显示成一行,接下来上例子,看看这个神奇的函数如何应用
准备测试数据
SQL> create table test(id number,name varchar2(20));
SQL> insert into test values(1,‘a‘);
SQL> insert into test values(1,‘b‘);
SQL> insert into test values(1,‘c‘);
SQL> insert into test values(2,‘d‘);
SQL> insert into test values(2,‘e‘);
SQL> commit;
效果1 : 行转列
SQL> select wm_concat(name) from test;
WM_CONCAT(NAME)
-------------------------------------------------------------------------
a,b,c,d,e
效果2: 把结果里的逗号替换成"|"
SQL> select replace(wm_concat(name),‘,‘,‘|‘) from test;
REPLACE(WM_CONCAT(NAME),‘,‘,‘|‘)
-----------------------------------------------------------------------
a|b|c|d|e
效果3:按ID分组合并name
SQL> select id,wm_concat(name) name from test group by id;
ID NAME
---------- ------------------------------
1 a,b,c
2 d,e
懒人扩展用法:
案例:我要写一个视图,类似"create or replace view as select 字段1,...字段50 from tablename" ,基表有50多个字段,要是靠手工写太麻烦了,有没有什么简便的方法? 当然有了,看我如果应用wm_concat来让这个需求变简单
SQL> select ‘create or replace view as select ‘|| wm_concat(column_name) || ‘ from dept‘from user_tab_columns where table_name=‘DEPT‘;
‘CREATEORREPLACEVIEWASSELECT‘||WM_CONCAT(COLUMN_NAME)||‘FROMDEPT‘
--------------------------------------------------------------------------------
create or replace view as select DEPTNO,DNAME,LOC from dept