mysql - 如何将 JOIN SQL 查询转换为关系代数？

Question

嗨，我希望得到帮助来解决一个非常烦人的问题。 我一直在思考这个问题，但我真的很难将这个 SQL 查询转换为其等效的关系代数查询。

查询:

SELECT
staff.STF_FirstNames AS `Doctor First Name`,
staff.STF_LastName AS `Doctor Last Name`,

patient.PAT_FirstNames AS `Patient First Name`,
patient.PAT_LastName AS `Patient Last Name`,

patient_makes_appointment.APP_DateTime AS `Appointment Time`

FROM staff
JOIN doctor                     ON staff.STF_ID = doctor.STF_ID
JOIN patient                    ON doctor.DOC_ID = patient.DOC_ID
JOIN patient_makes_appointment  ON patient.PAT_ID = patient_makes_appointment.PAT_ID

我对关系代数的基础知识很了解，但我很难了解如何用条件表示多个连接。

非常感谢任何建议，谢谢:)

Answer 1

也许你需要一些看起来像:

SELECT
  staff.STF_FirstNames AS `Doctor First Name`,
  staff.STF_LastName AS `Doctor Last Name`,

  patient.PAT_FirstNames AS `Patient First Name`,
  patient.PAT_LastName AS `Patient Last Name`,

  patient_makes_appointment.APP_DateTime AS `Appointment Time`

FROM staff, doctor, patient, patient_makes_appointment
WHERE staff.STF_ID = doctor.STF_ID 
  AND doctor.DOC_ID = patient.DOC_ID
  AND patient.PAT_ID = patient_makes_appointment.PAT_ID