Question

我对内部查询有疑问

架构：

DEPARTMENT（ deptnum ，descrip，instname，deptname，state，postcode）
ACADEMIC（ acnum ，deptnum *，famname，givename，姓名缩写，标题）
PAPER（ panum ，标题）
AUTHOR（ panum ，acnum **）
FIELD（ fieldnum ，id，title）
INTEREST（ fieldnum ，acnum **，descrip）

我有这种格式的输出：

select 
    acnum, title, givename, famname
from  
    academic a 
where 
    a.acnum in (select count(*) as no_of_papers, acnum 
                from author auth 
                join paper p on auth.panum = p.panum
                group by acnum 
                having count(*) < 20)
union
select 
    acnum, title, givename, famname
from 
    academic a 
where 
    a.acnum not in (select count(*) as no_of_papers, acnum 
                    from author auth 
                    join paper p on auth.panum = p.panum
                    group by acnum);

但是，除了外部查询的select语句中的字段外，我还希望结果集中的count(*)为no_of_papers。

我已经打破了很长一段时间了。

Answer 1

使用Join

尝试这样

SELECT acnum,title,givename,famname,no_of_papers
FROM academic a JOIN
( 
    SELECT COUNT(*) AS no_of_papers,acnum 
    FROM author auth JOIN paper p ON auth.panum=p.panum
    GROUP BY acnum HAVING COUNT(*)<20

)x ON 1 = 1
WHERE a.acnum IN (x.acnum)

UNION 

SELECT acnum,title,givename,famname,no_of_papers
FROM academic a 
(
    SELECT COUNT(*) AS no_of_papers,acnum 
    FROM author auth JOIN paper p ON auth.panum=p.panum
    GROUP BY acnum

 )y ON 1=1
WHERE a.acnum NOT IN (y.acnum)

Answer 2

我认为你不需要工会：

select 
  a.acnum,
  MIN(a.title),  -- only 1 value anyways if acnum is a primary key
  MIN(a.givename),
  MIN(a.famname),
  count(p.panum) as no_of_papers
from academic a
left join author auth on a.acnum = auth.acnum
left join paper p on auth.panum = p.panum
group by a.acnum
having 1 = 1 -- ??? no_of_papers < 20 ???
;

内部查询问题

2 个答案: