sql - 在 Oracle Sql 中添加 count 的结果

Question

我正在尝试两个表的元素数量，这是我尝试过的：

 select 
((select count(*) from Person,Professor where ID_Person = ID_Professor)  + 
(select count(*) from Person, Student where ID_Person = ID_Student ))

好吧，这不起作用任何想法我该怎么做？提前致谢

Answer 1

你只是from dual在最后遗漏了一个，使外部选择一个完整的语句。

和你一样，加上from dual：

select 
((select count(*) from Person,Professor where ID_Person = ID_Professor)  + 
(select count(*) from Person, Student where ID_Person = ID_Student ))
from dual

Answer 2

Wumpus Q. Wumbley 对 Oracle 数据库给出了正确的建议。

对于您的问题，您也可以尝试以下查询 -

   select sum(c_total) 
    from (
      select (select count(*) from professor 
               where professor.id_professor=person.id_person)
           + (select count(*) from student 
               where student.id_student=person.id_person) c_total
      from person
     group by person.id_person)