SQL Query - count - max

Question

我无法设法查询问题。我有三个表

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)); 

我的问题是：由单位从里斯本数量最多哪些deseases的名称（里斯本beeng的city从institute）。这是我想出来的，但它没有给我正确的答案。

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) 

作为一个例子：假设5个院所人与城市= '里斯本' 并与IID A，B，C，d，E respectevely（只是为了演示的目的，我知道类型是INT）; 5分类名称= Z，X，N，V，M的疾病。现在让我们说研究Z，X和M由研究机构A，B，C（以任何顺序）进行研究，研究N由D研究（1个），研究V由E研究（只有一个）。因此，通过任何里斯本学院学习deseases的最大数量为3（A，B和C都学习3个deseases），使表看起来像这样

Z - 3 
X - 3 
M - 3 

编辑：我设法找到一种方法来做到这一点。这里是我想出的查询

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

我不明白结构/问题，但我确实看到你在混合连接，并且有一个交叉连接，这会使得recrds数量膨胀。

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

只是一个粗略的猜测你需要什么：

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; 

这应该给你，在葡京机构的列表，并研究他们做了编号。

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; 

这给你一个病例列表和Lisboa instutitues的数量。

不幸的是，你的问题留下了很多猜测的空间，你需要什么 - 也许你应该添加一些示例数据和预期的结果。

Answer 3

这将返回开始与一个在里斯本机构的最大数量，走这在里斯本研究所疾病名称的列表：

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数研究机构，你需要从疾病影响表中的列的其余部分，你可以这样做（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