oracle wm_concat function for column to row, comma separated
--=== When the oracle version is not supported, use
SELECT id, listagg(a.name, ',') within group(order by id) as name
FROM tt1 a
group by a.id;
First let's take a look at this magical function wm_concat (column name), which can separate column values with "," signs and display them as a line. Next, let's take an example to see how this magical function is applied
Prepare test data
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;
Effect 1: row to column
SQL> select wm_concat(name) from test;
WM_CONCAT(NAME)
-------------------------------------------------------------------------
a,b,c,d,e
Effect 2: Replace the comma in the result with "|"
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