帶有兩個表的 MySQL 子查詢 count 和 group by

Question

我有醫院醫生表加入的醫生和醫院數據庫。

我必須列出城鎮，每個城鎮的醫院數量，但只有醫生超過 5 名的醫院。

SELECT hospital.town, count(town)
FROM hospital 
WHERE hospital.id = (
    SELECT count(hospital_id)
    FROM hospital_doctor GROUP BY hospital_id
    HAVING count(hospital_id)>5 )
GROUP BY town 

這是我的查詢，但 MySQL 返回給我，子查詢返回超過 1 行。

醫院

醫院醫生

我應該如何寫這個查詢？

Answer 1

你可以用基本相同的結構做你想做的事：

Select h.town, count(*)
from hospital h
where h.id in (select hd.hospital_id
               from hospital_doctor hd
               group by hd.hospital_id
               having count(*) > 5
              )
group by h.town ;

請注意以下事項：

• 您想in not =使用，因為子查詢可能返回多於一行。
• 子查詢應該返回醫院 id 而不是計數。
• 每當一個表引用多個表時，使用表別名和限定的列名。

Answer 2

Select hospital.town, count(town) 
from hospital 
where 
    hospital.id in ( 
        select hospital_id 
        from hospital_doctor 
        group by hospital_id 
        having count(hospital_id)>5 
    ) 
group by town

Answer 3

SELECT h.town,  count(h.town)
FROM 
(
    SELECT hospital_id
    FROM hospital_doctor GROUP BY hospital_id
    HAVING count(doctor_id)>5 
) s1 
left outer join hospital h on (s1.hospital_id=h.id)  
GROUP BY h.town