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我正在處理一個非常複雜的查詢，讓我試着向你解釋它。這裏是表，我在我的MySQL數據庫：MySQL LEFT OUTER JOIN虛擬表
學生表
--- `students` ---
student_id first_name last_name current_status status_change_date
------------ ------------ ----------- ---------------- --------------------
1 John Doe Active NULL
2 Jane Doe Retread 2012-02-01
students_have_courses表
--- `students_have_courses` ---
students_student_id courses_course_id s_date e_date int_date
--------------------- ------------------- ---------- ---------- -----------
1 1 2012-01-01 2012-01-04 2012-01-05
1 2 2012-01-05 NULL NULL
2 1 2012-01-10 2012-01-11 NULL
students_have_optional_courses表
--- `students_have_optional_courses` ---
students_student_id optional_courses_opcourse_id s_date e_date
--------------------- ------------------------------ ---------- ----------
1 1 2012-01-02 2012-01-03
1 1 2012-01-06 NULL
1 5 2012-01-07 NULL
這裏是我的查詢到目前爲止
SELECT
`students_and_courses`.student_id,
`students_and_courses`.first_name,
`students_and_courses`.last_name,
`students_and_courses`.courses_course_id,
`students_and_courses`.s_date,
`students_and_courses`.e_date,
`students_and_courses`.int_date,
`students_have_optional_courses`.optional_courses_opcourse_id,
`students_have_optional_courses`.s_date,
`students_have_optional_courses`.e_date
FROM (
SELECT
`c_s_a_s`.student_id,
`c_s_a_s`.first_name,
`c_s_a_s`.last_name,
`c_s_a_s`.courses_course_id,
`c_s_a_s`.s_date,
`c_s_a_s`.e_date,
`c_s_a_s`.int_date
FROM (
SELECT
`students`.student_id,
`students`.first_name,
`students`.last_name,
`students_have_courses`.courses_course_id,
`students_have_courses`.s_date,
`students_have_courses`.e_date,
`students_have_courses`.int_date
FROM
`students`
LEFT OUTER JOIN `students_have_courses`
ON (
`students_have_courses`.`students_student_id` = `students`.`student_id` AND ((
`students_have_courses`.`s_date` >= `students`.`status_change_date` AND
`students`.current_status = 'Retread') OR
`students`.current_status = 'Active')
)
WHERE
`students`.current_status = 'Active' OR
`students`.current_status = 'Retread'
) `c_s_a_s`
ORDER BY
`c_s_a_s`.`courses_course_id` DESC
) `students_and_courses`
LEFT OUTER JOIN `students_have_optional_courses`
ON (
`students_have_optional_courses`.students_student_id = `students_and_courses`.student_id AND
`students_have_optional_courses`.s_date >= `students_and_courses`.s_date AND
`students_have_optional_courses`.e_date IS NULL
)
GROUP BY
`students_and_courses`.student_id;
我想要返回的是所有Active或Retread學生的student_id，first_name和last_name，然後LEFT JOIN爲自s_date以來的最高course_id，s_date，e_date和int_date，因爲status_change_date如果狀態是'Retread'。然後LEFT JOIN最高optional_courses_opcourse_id，s_date和e_date從students_have_optional_courses表，其中students_have_optional_courses.s_date大於或等於students_have_courses.s_date和students_have_optional_courses.e_date IS NULL被返回是什麼
這裏：
student_id first_name last_name courses_course_id s_date e_date int_date optional_courses_opcourse_id s_date_1 e_date_1
------------ ------------ ----------- ------------------- ---------- ---------- ------------ ------------------------------ ---------- ----------
1 John Doe 2 2012-01-05 NULL NULL 1 2012-01-06 NULL
2 Jane Doe NULL NULL NULL NULL NULL NULL NULL
這裏是我想要返回什麼：
student_id first_name last_name courses_course_id s_date e_date int_date optional_courses_opcourse_id s_date_1 e_date_1
------------ ------------ ----------- ------------------- ---------- ---------- ------------ ------------------------------ ---------- ----------
1 John Doe 2 2012-01-05 NULL NULL 5 2012-01-07 NULL
2 Jane Doe NULL NULL NULL NULL NULL NULL NULL
一切工作，除了一兩件事，我似乎無法得到最高students_have_optional _courses.optional_courses_opcourse_id無論我如何形成查詢
對不起，我剛剛解決這個問題後寫了這一切，我認爲這有助於我想到的解決方案。
下面是解查詢：
SELECT
`students_and_courses`.student_id,
`students_and_courses`.first_name,
`students_and_courses`.last_name,
`students_and_courses`.courses_course_id,
`students_and_courses`.s_date,
`students_and_courses`.e_date,
`students_and_courses`.int_date,
`students_optional_courses`.optional_courses_opcourse_id,
`students_optional_courses`.s_date,
`students_optional_courses`.e_date
FROM (
SELECT
`c_s_a_s`.student_id,
`c_s_a_s`.first_name,
`c_s_a_s`.last_name,
`c_s_a_s`.courses_course_id,
`c_s_a_s`.s_date,
`c_s_a_s`.e_date,
`c_s_a_s`.int_date
FROM (
SELECT
`students`.student_id,
`students`.first_name,
`students`.last_name,
`students_have_courses`.courses_course_id,
`students_have_courses`.s_date,
`students_have_courses`.e_date,
`students_have_courses`.int_date
FROM
`students`
LEFT OUTER JOIN `students_have_courses`
ON (
`students_have_courses`.`students_student_id` = `students`.`student_id` AND ((
`students_have_courses`.`s_date` >= `students`.`status_change_date` AND
`students`.current_status = 'Retread') OR
`students`.current_status = 'Active')
)
WHERE
`students`.current_status = 'Active' OR
`students`.current_status = 'Retread'
) `c_s_a_s`
ORDER BY
`c_s_a_s`.`courses_course_id` DESC
) `students_and_courses`
LEFT OUTER JOIN (
SELECT
*
FROM
`students_have_optional_courses`
ORDER BY
`students_have_optional_courses`.optional_courses_opcourse_id DESC
) `students_optional_courses`
ON (
`students_optional_courses`.students_student_id = `students_and_courses`.student_id AND
`students_optional_courses`.s_date >= `students_and_courses`.s_date AND
`students_optional_courses`.e_date IS NULL
)
GROUP BY
`students_and_courses`.student_id;
然後添加您的解決方案作爲答案，請接受它。它可能會幫助其他人。 – fancyPants
感謝@tombom的+1 – amaster