Question

所以我正在修改考试，并在SQL河（或废弃地）中敲了一块大石头

我制作了下表并插入了以下数据：

create table Permissions
(
    fileName VARCHAR(40),
    userID VARCHAR (16),
    type VARCHAR(10),
    startdate DATE,
    duration NUMBER (5),
    constraint Pri_key PRIMARY KEY (userID,fileName)
);

create table Files
(
    name VARCHAR(20),
    fsize INT,
    numberofpermissions INT,
    constraints PRI_KEY2 PRIMARY KEY (name)
);

create table Users
(
    id VARCHAR(20),
    password VARCHAR (20),
    constraint Pri_key3 PRIMARY KEY (id)
);

-- after all tables create:
alter table Permissions
    add constraint Forn_key FOREIGN KEY (userID) REFERENCES Users(id)
    INITIALLY DEFERRED DEFERRABLE;
alter table Permissions
    add constraint Forn_key2 FOREIGN KEY (filename) REFERENCES Files(name)
    INITIALLY DEFERRED DEFERRABLE;
insert into Permissions VALUES ('Agenda','Jones','read','19-JAN-10',30);
insert into Permissions VALUES ('Agenda','Chun','read','19-JAN-10',30);
insert into Permissions VALUES ('Agenda','Rashid','write','17-JAN-10',50);
insert into Permissions VALUES ('Finance','Chun','write','05-DEC-09',50);
insert into Permissions VALUES ('AnnualReport','Jones','write','12-DEC-09',50);
insert into Users VALUES ('Jones', 'duck');
insert into Users VALUES ('Chun', 'tiger');
insert into Users VALUES ('Adams', 'shark');
insert into Users VALUES ('Rashid', 'puma');
insert into Files VALUES ('Agenda', 32, 3);
insert into Files VALUES ('FinanceTables',645, 0);
insert into Files VALUES ('Finance', 120, 1);
insert into Files VALUES ('AnnualReport', 1205, 1);
commit;

我现在正在尝试编写一个SQL命令来为每个拥有的用户显示总大小超过50的文件的权限：用户的权限 id，用户拥有权限的所有文件的总大小，以及用户的密码。

这是我到目前为止所做的，但是当我尝试添加任何内容来获取密码时，SQL +会出现一个异乎寻常的问题，我的屏幕上很快就会出现漏洞！

SELECT permissions.userID, sum(fsize) AS Totalsize
FROM files, permissions
where permissions.filename = files.name
group by permissions.userid
having SUM(fsize) > 50;

Answer 1

在oracle中，您需要通过

指定整个组

SELECT permissions.userID, users.password, sum(fsize) AS Totalsize
FROM files, permissions, users
where permissions.filename = files.name
and users.id = permissions.userID
group by permissions.userid, permissions.password
having SUM(fsize) > 50;

这与MySQL不同，其中可以隐含group by，但这更为正确。

Answer 2

加入用户表，并将密码添加到group by子句：

SELECT permissions.userID, users.password, sum(fsize) AS Totalsize
FROM files, permissions, users
where permissions.filename = files.name
and users.id = permissions.userID
group by permissions.userid, users.password
having SUM(fsize) > 50;

Answer 3

使用JOIN语法。它符合ANSI SQL。使用WHERE加入是一种不应再使用的旧语法。

SELECT
    u.id AS userid, u.password, SUM(f.fsize) AS Totalsize
FROM
    users u
    INNER JOIN permissions p
        ON u.id = p.userID    
    INNER JOIN files f
        ON p.filename = f.name
GROUP BY
    u.id, u.password
HAVING
    SUM(f.fsize) > 50;

请注意，基于聚合函数的条件必须放在HAVING子句中。 WHERE和HAVING子句之间的区别在于，在分组之前执行WHERE并在分组之后执行HAVING。

此外，GROUP BY子句必须包含SELECT列表中没有聚合函数的所有表达式。

Answer 4

这应该有效：

SELECT Users.id, Users.password, Totalsize
FROM Users
     INNER JOIN
     (SELECT userId, SUM(fSize) AS TotalSize
      FROM permissions
           INNER JOIN files ON permissions.filename = files.name
      group by permissions.userid
      having SUM(fsize) > 50) t ON t.userId = Users.Id

当然，这可以在没有内部连接的情况下完成，但是如果您需要更多字段，则可以更轻松地添加它们，而无需将额外字段添加到group by子句中。

SQL查询导致我睡眠不足

4 个答案: