oralce和db2兼容开发注意事项
投稿：lqh
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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