达梦数据库- 查询多行数据合并成一行数据

 

达梦 wm_concat函数，用于列转行，逗号分隔

 

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'