坚持编写这个嵌套子查询，被加入表的步骤弄糊涂了

Question

Employee(fname, minit, lname, SSN, bdate, address, sex, salary, superssn, dno); fname,minit,lname is the employee's name; bdate is birth date; superssn is supervisor's social security #; dno is dept #
Department(dname, DNUMBER, mgrssn, mgrstartdate); mgrssn is manager ssn
Dept_locations(DNUMBER, DLOCATION); dlocation is department location
Project(Pname, PNUMBER, plocation, dnum)
Works_on(ESSN, PNO, hours); ESSN is employee ssn, pno is project number
Dependent(ESSN, DEPENDENT_NAME, sex, bdate, relationship)

我想列出所有不在项目 7 工作且位于底特律的经理的姓氏和名字、SSN

这看起来不错：

Select e.ssn, e.lname, e.fname
from employee e, department d
where (d.mgrssn = e.ssn)

where e.ssn NOT in (
        select w.essn
        from works_on w
        where w.pno = '07'
        and p.plocation = 'Detroit'
)

我想我需要在 pno = 07 之前放置一个 pno =works_on 联合声明，但有人告诉我我不需要它。所以我现在真的很困惑。

我还需要在括号中包含 where (d.mgrssn = e.ssn) 吗？

Answer 1

这是带有连接的长格式查询：

select e.ssn, e.lname, e.fname
from employee e
  join works_on wo on wo.ESSN = e.ssn
  join project PO on po.pnumber = wo.pno
  join dept_location dl on dl.dnumber = po.dnum
where dl.dlocation != 'Detroit'
  or po.pnumber != 7

如果你想避免大量的连接，这里是一个带有 not in 的查询：

select e.ssn, e.lname, e.fname
from employee e
where e.ssn not in
(select wo.essn from works_on wo
  join dept_locations dl on dnumber = wo.pno
  where dl.dlocation = 'Detroit'
    or po.pnumber = 7)

希望对您有所帮助。