oralce和db2兼容开发注意事项

数据库兼容，在开发项目过程中，难免会遇到 更改数据库，或者后期 项目升级，也可能会遇到这种情况，这里就说明下oralce和db2兼容开发注意事项。

兼容oralce、db2开发注意事项（前提是db2版本是9.7，且是开启PLSQL编译选项之后创建的数据库)：

 1. 在like 之后若使用了表字段，应统一改成使用locate函数

如：
  oralce写法：
   select * from fw_right a where '03' like a.rightid||'%';
  兼容写法：
   select * from fw_right a where locate('03',a.rightid) = 1;
  oralce写法：
   select * from fw_right a where '03' like '%'||a.rightid||'%';
  兼容写法：
   select * from fw_right a where locate('03',a.rightid) > 0;

 2. 视图中使用的别名不应该与当前表字段同名

如以下语句，在Oracle中不会有问题，但在db2中会报"SQL0153N"错误：

 e.g:
  CREATE OR REPLACE VIEW V_WF_TODOLIST AS
     select c.process_def_id, c.process_def_name, a.action_def_id,
       a.work_item_id,  a.bae007,      a.action_def_name,
       a.state,     a.pre_wi_id,    a.work_type,
       a.operid,     a.x_oprator_ids,  b.process_key_info,
       to_char(to_date(a.start_time,  'yyyymmddhh24miss'),'yyyy-mm-dd hh24:mi:ss') as start_time,
       to_char(to_date(a.complete_time,'yyyymmddhh24miss'),'yyyy-mm-dd hh24:mi:ss') as complete_time,
       a.filter_opr, a.memo,a.bae002,a.bae003, a.bae006,c.x_action_def_ids
 from wf_work_item a, wf_process_instance b, wf_action_def c
  where a.action_def_id = c.action_def_id
  and b.process_def_id = c.process_def_id
  and a.bae007 = b.bae007
  and a.state in('0','2')

       兼容写法：

CREATE OR REPLACE VIEW V_WF_TODOLIST AS
  select c.process_def_id, c.process_def_name, a.action_def_id,
   a.work_item_id,  a.bae007,      a.action_def_name,
   a.state,     a.pre_wi_id,    a.work_type,
   a.operid,     a.x_oprator_ids,  b.process_key_info,
   to_char(to_date(a.start_time,  'yyyymmddhh24miss'),'yyyy-mm-dd hh24:mi:ss') as start_time_0,
   to_char(to_date(a.complete_time,'yyyymmddhh24miss'),'yyyy-mm-dd hh24:mi:ss') as complete_time_0,
   a.filter_opr, a.memo,a.bae002,a.bae003, a.bae006,c.x_action_def_ids
   from wf_work_item a, wf_process_instance b, wf_action_def c
   where a.action_def_id = c.action_def_id
   and b.process_def_id = c.process_def_id
   and a.bae007 = b.bae007
   and a.state in('0','2')

   3.在下列情况下不允许 ORDER BY 或 FETCH FIRST n ROWS ONLY： 

*  外层全查询视图
  *  "SQL 表函数"的 RETURN 语句中的外层全查询
  *  具体化查询表定义
  *  未用圆括号括起来的子查询

否则会报"SQL20211N  规范 ORDER BY 或 FETCH FIRST n ROWS ONLY 无效。"错误.

e.g:
  oralce写法：

  CREATE OR REPLACE VIEW V_FW_BLANK_BULLETIN as
  select id,   bae001, operunitid, operunittype, unitsubtype, ifergency,
    title, content, digest,  duetime,   validto,   aae100,
    bae006, bae002, bae003,  id as colid,
    substr(digest,1,20) as digest2
   from fw_bulletin
  where duetime <= to_char(sysdate,'yyyymmddhh24miss')
   and (to_char(validto) >= to_char(sysdate,'yyyymmddhh24miss') or validto is null)
   and aae100 ='1'
  order by ifergency desc, id desc, duetime desc

      兼容写法：

  CREATE OR REPLACE VIEW V_FW_BLANK_BULLETIN as
  select * from (select id,   bae001, operunitid, operunittype, unitsubtype, ifergency,
   title, content, digest,  duetime,   validto,   aae100,
   bae006, bae002, bae003,  id as colid,
   substr(digest,1,20) as digest2
  from fw_bulletin
  where duetime <= to_char(sysdate,'yyyymmddhh24miss')
  and (to_char(validto) >= to_char(sysdate,'yyyymmddhh24miss') or validto is null)
  and aae100 ='1'
  order by ifergency desc, id desc, duetime desc)

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