跨越3個表

Question

這裏的Oracle SQL檢索數據的關係：

CREATE TABLE employee (
    name varchar2(15) not null, 
    ssn  char(9), 
    primary key (ssn), 
    foreign key (superssn) references employee(ssn), 
); 

CREATE TABLE project (
    pname  varchar2(15) not null, 
    pnumber number(4), 
    primary key (pnumber), 
    unique (pname), 
); 

CREATE TABLE works_on (
    essn char(9), 
    pno number(4), 
    primary key (essn,pno), 
    foreign key (essn) references employee(ssn), 
    foreign key (pno) references project(pnumber) 
); 

問：誰檢索每個項目工作的所有員工的姓名。

我想我被要求查詢所有參與項目的員工，按項目名稱排序。任何想法如何解決這個問題？

Answer 1

這是一個經典divide問題。

試試這個。

SELECT name FROM Employee 
    WHERE NOT EXISTS (SELECT pnumber FROM project WHERE pnumber 
     NOT IN (SELECT pno from Works_on WHERE employee.ssn = works_on.essn)) 

或所有項目和自己的員工，

SELECT employees.name, project.pname FROM employees 
    INNER JOIN works_on ON employees.ssn = works_on.essn 
     INNER JOIN project ON works_on.pno = project.pnumber; 

Answer 2

SELECT E.NAME FROM 
EMPLOYEE E, 
PROJECT P, 
WORKS_ON WO 
WHERE 
E.SSN = WO.ESSN 
AND WO.PNO = P.PNUMBER 
ORDER BY P.PNAME; 

檢查是否適用於您。

你可以試試這個太：

SELECT E.NAME FROM 
(SELECT E.NAME, P.PNAME FROM 
    EMPLOYEE E, 
    PROJECT P, 
    WORKS_ON WO 
    WHERE 
    E.SSN = WO.ESSN 
    AND WO.PNO = P.PNUMBER 
    ORDER BY P.PNAME);