[英]Left Outer Join in sql query
数据库:
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
...
查找从事3个或更多项目且不在克利夫兰的经理的姓氏和SSN。
这是我到目前为止的内容:
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
做对group by
? 是否应将此代码分为两个部分,例如循环?
选择JOIN
查找员工的所有项目
首先, HAVING
告诉您此用户在'Cleveland'
没有项目
第二个HAVING
告诉您该用户有3个项目或更多
。
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
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