wmsys.wm_concat的几个用法

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今天才发现了wmsys.wm_concat这个有趣有用的函数，它的作用是以','链接字符。

例子如下：

SQL> create table idtable (id number,name varchar2(30));

Table created

SQL> insert into idtable values(10,'ab');

1 row inserted

SQL> insert into idtable values(10,'bc');

1 row inserted

SQL> insert into idtable values(10,'cd');

1 row inserted

SQL> insert into idtable values(20,'hi');

1 row inserted

SQL> insert into idtable values(20,'ij');

1 row inserted
SQL> insert into idtable values(20,'mn');

1 row inserted

SQL> select * from idtable;

        ID NAME
---------- ------------------------------
        10 ab
        10 bc
        10 cd
        20 hi
        20 ij
        20 mn

6 rows selected
SQL> select id,wmsys.wm_concat(name) name from idtable
2 group by id;

        ID NAME
---------- --------------------------------------------------------------------------------
        10 ab,bc,cd
        20 hi,ij,mn

SQL> select id,wmsys.wm_concat(name) over (order by id) name from idtable;

        ID NAME
---------- --------------------------------------------------------------------------------
        10 ab,bc,cd
        10 ab,bc,cd
        10 ab,bc,cd
        20 ab,bc,cd,hi,ij,mn
        20 ab,bc,cd,hi,ij,mn
        20 ab,bc,cd,hi,ij,mn

6 rows selected

SQL> select id,wmsys.wm_concat(name) over (order by id,name) name from idtable;

        ID NAME
---------- --------------------------------------------------------------------------------
        10 ab
        10 ab,bc
        10 ab,bc,cd
        20 ab,bc,cd,hi
        20 ab,bc,cd,hi,ij
        20 ab,bc,cd,hi,ij,mn

6 rows selected

个人觉得这个用法比较有趣.

SQL> select id,wmsys.wm_concat(name) over (partition by id) name from idtable;

        ID NAME
---------- --------------------------------------------------------------------------------
        10 ab,bc,cd
        10 ab,bc,cd
        10 ab,bc,cd
        20 hi,ij,mn
        20 hi,ij,mn
        20 hi,ij,mn

6 rows selected

SQL> select id,wmsys.wm_concat(name) over (partition by id,name) name from idtable;

        ID NAME
---------- --------------------------------------------------------------------------------
        10 ab
        10 bc
        10 cd
        20 hi
        20 ij
        20 mn

6 rows selected