select nvl(variable.varName,null),nvl(History.value,null),nvl(History.Date,null) from variable,History where variable.varID=(select nvl(varID,null) from (select * from History order by Date desc) where rownum=1)
调试欢乐多
variable表中肯定是有记录的,但history表中可能没有相应的记录,我现在希望这样,如果history表中没有相应记录,则作联合查询后,history的字段以null表示..感觉有点像左外连接..
full join History b on a.varID=b.varID;
left join History b on a.varID=b.varID;谢谢两位了,接分..