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以下 SQL 查询的目标是返回居住在 San Fran 或 LA 的每位女性经理的姓名和薪水。我很困惑为什么这个查询会返回男性经理和女性经理......我最初认为定义约束“gender ='F'”以及自然加入会摆脱所有男性经理立即上市。

select Lastname, FirstName, MidInitial, salary, gender
  from Employee natural join Works natural join Manages
where Lastname = ManagerLastname and
FirstName = MFirstName and
MidInitial = MMidInitial and
gender = 'F' and
city = 'San Fran' or city = 'LA';

--RESULT:
LASTNAME    FIRSTNAME   MIDINITIAL  SALARY  GENDER
Brandy      Dan         L           42000   M
Clemson     Ann         M           39000   F
Gill        Mary        L           48700   F
Simon       Eric        K           45000   M

有没有人认为上述查询有任何本质上的错误？仅供参考：这是该数据库表的架构：

create table Employee(
    Lastname    varchar(10),
    FirstName   varchar(10),
    MidInitial  char(1),
    gender      char(1),
    street      varchar(10),
    city        varchar(10),
    primary key(Lastname, FirstName, MidInitial));

create table company(
    company_name    varchar(20),
    city    varchar(10),
    primary key(company_name));

create table Works(
    Lastname    varchar(10),
    FirstName   varchar(10),
    MidInitial  char(1),
    company_name    varchar(20),
    salary      numeric(8,2),
    primary key(Lastname, FirstName, MidInitial, company_name),
    foreign key(Lastname, FirstName, MidInitial) references Employee,
    foreign key(company_name) references company);

create table Manages(
    Lastname    varchar(10),
    FirstName   varchar(10),
    MidInitial  char(1),
    ManagerLastname varchar(10),
    MFirstName  varchar(10),
    MMidInitial char(1),
    start_date  date,
    primary key(Lastname, FirstName, MidInitial, ManagerLastname, MFirstName, MMidInitial),
    foreign key(Lastname, FirstName, MidInitial) references Employee);

另外，我正在为 Oracle 11g R2 使用 SQL。

谢谢你看看这个！

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1 回答 1

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问题是它AND的优先级高于OR.

因此，您的查询实际上是：

显示Lastname = ManagerLastname and FirstName = MFirstName and MidInitial = MMidInitial and gender = 'F' and city = 'San Fran' 的所有记录

- 或者 -

城市 = '洛杉矶'

你想要的是：

where Lastname = ManagerLastname and
FirstName = MFirstName and
MidInitial = MMidInitial and
gender = 'F' and
( city = 'San Fran' or city = 'LA' )
于 2013-09-22T20:47:52.183 回答