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我的问题是：对于每个会议，如果会议在 2012 年 7 月 1 日之前举行，则显示会议标题和“第一学期”字样，如果会议在 2012 年 7 月 1 日或之后举行，则显示“第二学期”字样。对于包含“First term”或“Second term”字样的列，请制作标题术语。与之关联的表是

CONFID             TITLE                    LOCATION          SDATE
------        --------------------       -------------------- ---------
c00001    Hydroinformatics                  Singapore          15-JUN-12
c00002    Ecological_modeling                Berlin            15-JUL-12
c00003    Computational_M                    London            25-MAY-12
c00004    Ecoinformatics                     Boston            22-AUG-12
c00005    Uncertainty_analysis               Athens            10-OCT-12
c00006    Large_databases                    Toronto           13-APR-12
c00007    Systems_analysis                    Boston           23-MAR-12
c00008    Systems_integration                 Tokyo            24-FEB-12
c00009    Aquatic_biology                      Helsinki        12-MAY-12
c00010    Information_systems                   Paris          08-JAN-12
c00011    Simulation_modeling                   Rome           01-SEP-12
c00012    DSS                                  Melbourne       18-DEC-12

我写的sql语句是：

select C.Title, 'First term' as "Term" 
from Conference_C C 
where C.ConfID in (select C.Sdate 
                   from Conference_C C 
                   where C.Sdate < '1-July-12') 
union 
select C.Title, 'Second term' as "Term" 
from Conference_C C 
where C.ConfID in (select C.Sdate 
                     from Conference_C C 
                     where C.Sdate >= '1-July-12');

我收到以下错误：

select C.Title, 'First term' as "Term" from Conference_C C where C.ConfID
                                                                 *
ERROR at line 1:
ORA-01858: a non-numeric character was found where a numeric was expected

请澄清我哪里出错了，任何帮助将不胜感激。谢谢你

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1 回答 1

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您正在将ConfID(a number) 与Sdate从内部查询返回的 (a date) 进行比较：

where C.ConfID in (select C.Sdate 
                   from Conference_C C 
                   where C.Sdate < '1-July-12')

您只需要一个简单的 SQL，如下所示：

select C.Title, 'First term' as "Term" 
from Conference_C C 
where C.Sdate < '1-July-12'
union
select C.Title, 'Second term' as "Term" 
from Conference_C C 
where C.Sdate >= '1-July-12'

另外由于这两个部分union是互斥的，所以union all可以使用 a （它的性能更好，因为它不必消除重复）

于 2013-03-26T16:43:21.053 回答