同时使用Union和Order by问题(ORA-00933错误)解决

之前，同事在编写视图的过程中遇到这样了这个错误。我把简化后的语句整理如下：

   1: select

   2: '2016' as nf,

   3: qxdm,

   4: round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

   5: from dltb_2016@dblink_td_tdxz m where dlmc='城市'

   6: group by m.qxdm order by m.qxdm

   7:  

   8: union all 

   9:  

  10: select

  11: '2017' as nf,

  12: qxdm,

  13: round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

  14: from dltb_2017@dblink_td_tdxz n where dlmc='城市'

  15: group by n.qxdm order by n.qxdm

主要是查询各个管辖区中2016年和2017年地类图斑数据中城市用地的面积，语句分单块均可以执行成功，但是使用UNION后则出现ora-00933错误。

检查了列的数量、数据格式均保持一致，没有不对应的现象。

追查了一下原因，最终发现是union和order by字句引起的。

最终处理方式参考如下：

1、如果排序没必要，可以直接去掉，或者在union后统一排序

   1: select

   2: '2016' as nf,

   3: qxdm,

   4: round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

   5: from dltb_2016@dblink_td_tdxz m where dlmc='城市'

   6: group by m.qxdm 

   7:  

   8: union all 

   9:  

  10: select

  11: '2017' as nf,

  12: qxdm,

  13: round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

  14: from dltb_2017@dblink_td_tdxz n where dlmc='城市'

  15: group by n.qxdm

或者

   1: select

   2: '2016' as nf,

   3: qxdm,

   4: round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

   5: from dltb_2016@dblink_td_tdxz m where dlmc='城市'

   6: group by m.qxdm 

   7:  

   8: union all 

   9:  

  10: select

  11: '2017' as nf,

  12: qxdm,

  13: round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

  14: from dltb_2017@dblink_td_tdxz n where dlmc='城市'

  15: group by n.qxdm order by qxdm

2、可以再嵌套一层查询

   1: select * from (

   2: select

   3: '2016' as nf,

   4: qxdm,

   5: round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

   6: from dltb_2016@dblink_td_tdxz m where dlmc='城市'

   7: group by m.qxdm order by m.qxdm

   8: )

   9:  

  10: union all 

  11:  

  12: select * from (

  13: select

  14: '2017' as nf,

  15: qxdm,

  16: round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

  17: from dltb_2017@dblink_td_tdxz n where dlmc='城市'

  18: group by n.qxdm order by n.qxdm

  19: )

或者

   1: with

   2:  s1 as (

   3:  select

   4:        '2016' as nf,

   5:        qxdm,

   6:        round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

   7:        from dltb_2016@dblink_td_tdxz m where dlmc='城市'

   8:        group by m.qxdm order by m.qxdm

   9:   ),

  10:   s2 as (

  11:   select

  12:      '2017' as nf,

  13:      qxdm,

  14:      round(sum(tbdlmj)/10000,2) as csydmj--单位转换，2位小数

  15:      from dltb_2017@dblink_td_tdxz n where dlmc='城市'

  16:      group by n.qxdm order by n.qxdm

  17:   )

  18:   select * from s1

  19:   union all

  20:   select * from s2;