关系代数帮助

Question

我是关系代数的新手，发现它很困难。我已经回答了几个问题；但是，它们相对简单。不过可以帮助解决这些问题。

数据库

Patient (PatientCode, PatientSurname, PatientFirstname, PatientSex, PatientAge,
         PatientOccupation, PatientHeight, PatientWeight, PatientAddress) 

Doctor (DoctorCode, DoctorSurName,  DoctorFirstName, DoctorPrivateAddress,
        MobileNo, Doctor Specialisim) 

Operation (Operation Code, PatientCode, DoctorCode, Date, Time, Result,
           OperationType) 

Is_Seen_By (PatientCode, DoctorCode, Date, Time)

查询

1. 查找“DR333”医生做过手术且结果未成功的患者的姓氏和性别。

2. 查找已在 2010 年 11 月 18 日完成并成功的操作的代码。另请列出参与手术的医生姓名。

Answer 1

这可能完全错误，也可能不完全错误，我从一个很长的电脑假期回来了。它的 SQL 应该是这样的：

第一季度：

SELECT Patient.PatientSurname, Patient.PatientSex
  FROM Patient INNER JOIN Operation
    ON Operation.PatientCode = Patient.PatientCode
 INNER JOIN DOCTOR ON Operation.DoctorCode = Doctor.DoctorCode
 WHERE Operation.Result = "fail"
   AND Doctor.DoctorCode = "DR333"

第二季度：

SELECT Operation.OperationCode, Doctor.DoctorFirstName
  FROM Operation INNER JOIN Doctor ON Operation.DoctorCode = Doctor.DoctorCode
 WHERE Operation.Date = "18/11/2010"
   AND Operation.Result = "success"