內部查詢問題

Question

我有一個關於內部查詢疑問

模式：

• DEPARTMENT（deptnum，記述，instname，則將DEPTNAME，州，郵編）
• ACADEMIC（acnum ，deptnum *，famname，givename，首字母縮寫，標題）
• PAPER（panum，標題）
• AUTHOR（panum，acnum **）
• FIELD（fieldnum，ID，標題）
• INTEREST（fieldnum，acnum **，記述）

我有這種格式的輸出：

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，除了外部查詢的select語句中的字段外，我還希望在結果集中使用count(*)作爲no_of_papers。

我已經打破了我的頭很長一段時間了。

Answer 1

使用Join

嘗試像這樣

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

我不認爲你需要一個聯盟：

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 ??? 
;