union查询不工作，导致ORA-00904错误

Question

我已经创建了两个表，uview和vview。

CREATE TABLE  Uview
(   USERID CHAR(6) NOT NULL ENABLE, 
pageID varCHAR2(50) NOT NULL ENABLE, 
VISIT_TIME TIMESTAMP (6) NOT NULL ENABLE, 
view_TIME TIMESTAMP (6) NOT NULL ENABLE, 
fview_TIME TIMESTAMP (6) NOT NULL ENABLE, 
entry varCHAR2(50) NOT NULL ENABLE, 
exit varCHAR2(50) NOT NULL ENABLE, 
 PRIMARY KEY (USERID, VISIT_TIME,viewtime) ENABLE )


CREATE TABLE  vview
 (  VISITORID CHAR(8) NOT NULL ENABLE, 
    pageID varCHAR2(50) NOT NULL ENABLE, 
VISIT_TIME TIMESTAMP (6) NOT NULL ENABLE, 
view_TIME TIMESTAMP (6) NOT NULL ENABLE, 
fview_TIME TIMESTAMP (6) NOT NULL ENABLE, 
entry varCHAR2(50) NOT NULL ENABLE, 
exit varCHAR2(50) NOT NULL ENABLE, 
 PRIMARY KEY (visitorID, VISIT_TIME,view_time) ENABLE )

select userID,pageID,visit_time,view_time,fview_time,exit,entry
    from uview 
union
select visitorid,pageID,visit_time,view_time,fview_time,exit,entry
    from vview;

然而，有一个错误ORA-00904："ENTRY"：无效的标识符。即使我从查询ORA-00904："Exit"：invalid identifier中删除了条目，结果也是无效的。这对我来说太奇怪了。请告诉我出了什么问题。谢谢。

Answer 1

Entry是Oracle中的保留字：http://docs.oracle.com/cd/B19306_01/em.102/b40103/app_oracle_reserved_words.htm。你必须用双倍数来转义它：

SELECT .... , "entry"
FROM uview
etc...