左外連接SQL查詢

Question

數據庫：

EMPLOYEE (fname, minit, lname, ssn, birthdate, address, sex, salary, superssn, dno)     KEY: ssn
DEPARTMENT (dname, dnumber, mgrssn, mgrstartdate)               KEY: dnumber.
PROJECT  (pname, pnumber, plocation, dnum)                          KEY: pnumber.
WORKS_ON (essn, pno, hours)                                         KEY: (essn, pno)
DEPENDENT  (essn, dependent-name, sex, bdate, relationship)             KEY: (essn, dependent-name)

我想使用left outer join和group by ...
查找從事3個或更多項目且不在克利夫蘭的經理的姓氏和SSN。

這是我到目前為止的內容：

select Lname
  from Employee e outer join Department d
where (e.ssn = d.mgrssn) 
   and  ssn NOT in (
                      select  w.essn
                       from   works_on w outer join Project p
                      where w.pno = p.pnumber
                          and  p.plocation = 'Cleveland'
                      group by w.essn
                      having count(*) >= 3
                     )

我是否使用left outer join和group by做對group by ？ 是否應將此代碼分為兩個部分，例如循環？

Answer 1

選擇JOIN查找員工的所有項目

首先， HAVING告訴您此用戶在'Cleveland'沒有項目

第二個HAVING告訴您該用戶有3個項目或更多

。

SELECT e.Lname, e.ssn
FROM Employee e   
JOIN works_on w
  ON e.ssn = w.essn
JOIN Project p
  ON w.pno = p.pnumber
GROUP BY e.ssn
HAVING 
     SUM(CASE WHEN p.plocation = 'Cleveland' THEN 1 ELSE 0 END) = 0
AND  COUNT(*) >= 3