把字符串1,2,3,4,5,以逗号分隔,输出为行,也就是12345随手写了一个,Oracle10G以上有表如下SQLselect*fromt;IDNAM..
把字符串 '1,2,3,4,5',以逗号分隔,输出为行,也就是
1
2
3
4
5
随手写了一个, Oracle 10G 以上
有表如下
ID NAME
---------- --------
1 0
1 1
1 5
1 2
1 8
1 10
2 9
2 7
2 8
3 你好
3 他好
3 大家好
12 rows selected.
然后客户那反馈说数据库说9i的,报错说connect by不能使用子查询。
于是再稍做修改,在确定逗号不会超过99个的前提下,直接写个常量100,可以支持9i
后来想想这样也不好,于是建议建立一张特定的IOT表,保存10000个数字,一般够用了。
建立一张IOT,共10000行,同样支持9i
然后不再需要常量100,即保证准确,又保证较好的性能
ID NAME
---------- --------
1 0
1 1
1 5
1 2
1 8
1 10
2 9
2 7
2 8
3 你好
3 他好
3 大家好
12 rows selected.
下面测试一下性能:转换50万行试试,美国服务器,测试环境:DELL D630 用了4年半的旧笔记本,磁盘都是碎片
SQL> insert into t select rownum+4,'1,2,3,4' from dual connect by rownum
500000 rows created.
SQL> commit;
Commit complete.
set timi on
SQL> set timi on
SQL> create table t500 nologging as
with vmaxnum as (
select ele
from tnumber
where ele
select id,
decode(pos,0,substr(name,lagpos+1),substr(name,lagpos+1,pos-lagpos-1)) name
from (select id,name,ele,pos,nvl(lag(pos) over (partition by id order by ele),0) lagpos
from (select id,name,ele,
instr(name,',',1,ele) pos
from (select /*+ all_rows no_merge(v2) use_merge(t,v2) */
t.id,t.name,v2.ele
from t,vmaxnum v2
where ele
order by id,ele;
Table created.
Elapsed: 00:00:16.48
耗时16秒,香港服务器,含建表的写盘时间
SQL> select count(*) from t500;
COUNT(*)
----------
2000012
当然还有别的写法,比如简单的可以这样
或者10G以上用正则表达式也可以实现
这个方法可能不是最高效的,但也还可以。
这个SQL的性能和字符串含有的逗号的个数有关,逗号越多,也就是分隔项越多,性能越差。
本文出自 “专注J2EE系列规范下的..” 博客,请务必保留此出处
,美国空间
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