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HomeDatabaseMysql Tutorial Oracle数据库9i、10g里列转行各种方法比较

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

  • create table tnumber(ele,constraint pk_tnumber primary key(ele)) organization index as 
  • select rownum id from dual connect by rownum=10000; 
  • 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。

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