从 3 个带有 IN 子句的表中选择答案

【问题标题】：Select from 3 tables with IN clause从 3 个带有 IN 子句的表中选择
【发布时间】：2019-11-11 16:58:53
【问题描述】：

需要显示下一个：来自表用户名的所有 fNAME 和 lNAME，其位置为“Admin”并在 'ABC' 公司 (NAME_COMPANY) 工作，带有 IN 子句。

create table company 
(
    CODE_COMPANY char(30),
    NAME_COMPANY varchar2(30) not null,
    MAIL_COMPANY varchar2(30) null,

    constraint PK_CODE_COMPANY primary key (CODE_COMPANY),
);

create table USERNAME 
(
    NAME_USERNAME varchar2(30),
    USER_LOCATION number,
    fNAME varchar2 (30) not null,
    lNAME varchar2 (30) not null,
    PHONE_USER char(13) null,
    USER_POSITION varchar2 (30),
    check (USER_POSITION in('Admin', 'Superadmin', 'Technician', 'Student')),

    constraint PK_NAME_USERNAME primary key (NAME_USERNAME),
    constraint FK_USER_LOCATION foreign key (USER_LOCATION) references uLOCATION (LOCATION)
);

create table uLOCATION 
(
    LOCATION number,
    CODE_COMPANY char(30),
    NAME_LOCATION varchar2(30) not null,
    FLOOR_LOCATION varchar2(10),
    check (FLOOR_LOCATION in ('MAIN_FLOOR', '1ST FLOOR', '2ND FLOOR', '3RD FLOOR')),

    constraint PK_LOCATION primary key (LOCATION),
    constraint FK_CODE_COMPANY_L foreign key (CODE_COMPANY) references company (CODE_COMPANY),
);

【问题讨论】：

标签： sql in-clause

【解决方案1】：

我想你正在寻找：

select u.*
from username u
where u.user_position = 'admin' and
      u.ulocation in (select l.location
                      from ulocation l join
                           ucompany c
                           on l.code_company = c.code_company
                      where c.name_company = 'ABC'
                     );

【讨论】：

【解决方案2】：

如果我正确理解您的问题，您需要以下查询。不知道为什么你会使用 IN 而不是标准 = 但是我已经将两者都包含在一个评论中。

select
    user.fName,
    user.lName
from
    username as user
    inner join ulocation as location
        on location.location = user.user_location
    inner join company as company
        on company.code_company = location.code_company
where
    user.user_position = 'Admin'
    and name_company in ('A','B','C') -- not needed if only checking for one company
                                      -- if only one company, change to: name_company = 'ABC'

【讨论】：

需要使用IN代替inner join。有可能吗？