SQL Query - count - max

Question

我無法設法查詢問題。我有三個表

CREATE TABLE institute (
    iid INT PRIMARY KEY, 
    sign VARCHAR(127) UNIQUE, 
    city VARCHAR(127) NOT NULL, 
    area INT CHECK (area>0)); 

CREATE TABLE desease (
    did INT PRIMARY KEY, 
    name VARCHAR(127) UNIQUE, 
    level INT CHECK (level>0)); 

CREATE TABLE studies (
    did INT, 
    iid INT, 
    FOREIGN KEY (did) REFERENCES desease (did), 
    FOREIGN KEY (iid) REFERENCES institute (iid), 
    PRIMARY KEY (iid,did)); 

我的問題是：由單位從里斯本數量最多哪些deseases的名稱（里斯本beeng的city從institute）。這是我想出來的，但它沒有給我正確的答案。

SELECT DISTINCT D.name, MAX(I.iid) 
    FROM desease D, studies S 
    JOIN institute I ON (S.iid = I.iid) 
WHERE I.city = 'Lisboa' AND D.did = S.did 
GROUP BY D.nome 
HAVING COUNT(I.iid) = MAX(I.city) 

作爲一個例子：假設5個院所人與城市= '里斯本' 並與IID A，B，C，d，E respectevely（只是爲了演示的目的，我知道類型是INT）; 5分類名稱= Z，X，N，V，M的疾病。現在讓我們說研究Z，X和M由研究機構A，B，C（以任何順序）進行研究，研究N由D研究（1個），研究V由E研究（只有一個）。因此，通過任何里斯本學院學習deseases的最大數量爲3（A，B和C都學習3個deseases），使表看起來像這樣

Z - 3 
X - 3 
M - 3 

編輯：我設法找到一種方法來做到這一點。這裏是我想出的查詢

SELECT DISTINCT D.name, COUNT(*) AS C 
FROM desease D, studies E, institute I 
WHERE I.iid = E.iid AND D.did = E.did AND I.city = "Lisboa" 
GROUP BY D.name 
HAVING C >= ALL (
SELECT COUNT(*) 
FROM desease D, studies E, institute I 
WHERE I.iid = E.iid AND D.did = E.did AND I.cidade = "Lisboa" 
GROUP BY D.name 

）;

Answer 1

我不明白結構/問題，但我確實看到你在混合連接，並且有一個交叉連接，這會使得recrds數量膨脹。

SELECT DISTINCT D.name, MAX(I.iid) 
FROM desease D 
INNER JOIN studies S ON D.iid=S.Did 
INNER JOIN institute I ON (S.iid = I.iid) 
WHERE I.city = 'Lisboa' AND D.did = S.did 
GROUP BY D.nome 
HAVING COUNT(I.iid) = MAX(I.city) 

Answer 2

只是一個粗略的猜測你需要什麼：

SELECT stu.iid, COUNT(*) AS nstudies 
FROM studies stu, institute ins 
WHERE stu.iid=ins.iid 
AND ins.city='Lisboa' 
GROUP BY stu.iid 
ORDER BY nstudies DESC; 

這應該給你，在葡京機構的列表，並研究他們做了編號。

SELECT stu.did, COUNT(*) AS ninst 
FROM studies stu, institute ins, disease dis 
WHERE stu.iid=ins.iid 
AND stu.did=dis.did 
AND ins.city='Lisboa' 
GROUP BY stu.did 
ORDER BY ninst DESC; 

這給你一個病例列表和Lisboa instutitues的數量。

不幸的是，你的問題留下了很多猜測的空間，你需要什麼 - 也許你應該添加一些示例數據和預期的結果。

Answer 3

這將返回開始與一個在里斯本機構的最大數量，走這在里斯本研究所疾病名稱的列表：

SELECT D.name, COUNT(*) as numberOfInstitutes 
FROM desease D 
INNER JOIN studies S ON D.did=S.did 
INNER JOIN institute I ON (S.iid = I.iid) 
WHERE I.city = 'Lisbon' 
GROUP BY D.did 
ORDER BY COUNT(*) desc 

如果您只需要具有一大多數研究機構，你需要從疾病影響表中的列的其餘部分，你可以這樣做（在SQL Server）：

SELECT TOP 1 D.* 
FROM desease D 
INNER JOIN 
(
    SELECT D.did, COUNT(*) as numberOfInstitutes 
    FROM desease D 
    INNER JOIN studies S ON D.did=S.did 
    INNER JOIN institute I ON (S.iid = I.iid) 
    WHERE I.city = 'Lisbon' 
    GROUP BY D.did 
) as tblCount on tblCount.did = D.did 
ORDER BY numberOfInstitutes desc