SQL嵌套式查詢作業SQL小提琴

Question

找到最大成員（患者）數量的保險公司。

這就是數據庫和我第一次嘗試更貼近：

http://sqlfiddle.com/#!3/4b2ed/27

SELECT P.cid AS cid, COUNT (P.pid) AS CountP 
FROM  Patient P 
GROUP BY P.cid 

如何獲得最大countp？

Answer 1

只是爲了你的結果降序的病例數，並只取第一條記錄。

SELECT P.cid AS cid, COUNT(P.pid) AS CountP 
FROM  Patient P 
GROUP BY P.cid 
ORDER BY CountP DESC 
LIMIT 1 

如果不止一家保險公司可能有成員是最大的號碼，你想獲取所有的人，你將需要使用子查詢：

SELECT P.cid AS cid, COUNT(P.pid) AS CountP 
FROM  Patient P 
GROUP BY P.cid 
HAVING  CountP = (
    SELECT COUNT(pid) AS c 
    FROM  Patient 
    GROUP BY cid 
    ORDER BY c DESC 
    LIMIT 1 
); 

在你描述的怪現狀在您的意見，其中一個是無法使用LIMIT，你可以這樣做：

SELECT P.cid AS cid, COUNT(P.pid) AS CountP 
FROM  Patient P 
GROUP BY P.cid 
HAVING  CountP = (SELECT MAX(d.c) FROM (
    SELECT COUNT(pid) AS c 
    FROM  Patient 
    GROUP BY cid 
) AS d); 

Answer 2

嘗試用以下：
最大（計數（P.pid））

Answer 3

SELECT P.cid, COUNT (P.pid) AS CountP 
FROM Patient P 
GROUP BY P.cid 
compute max(count(p.pid)) 

Answer 4

哇 - 很多限制。在這裏你去：

SELECT MAX(CountP) FROM (
    SELECT P.cid, COUNT (P.pid) AS CountP 
    FROM Patient P 
    GROUP BY P.cid 
) winner