将2个SQL查询与公共字段和AVG合并

Question

我的SQL在没有研究它2年后有点生疏，所以我无法找到一种方法来执行此操作。

我需要从Moodle数据库获取一些数据，即学生评定其教师的反馈测试的平均值。

此SQL查询：

SELECT mdl_course.id, mdl_user.username FROM mdl_course 
INNER JOIN mdl_context ON mdl_context.instanceid = mdl_course.id 
INNER JOIN mdl_role_assignments ON mdl_context.id = mdl_role_assignments.contextid 
INNER JOIN mdl_role ON mdl_role.id = mdl_role_assignments.roleid 
INNER JOIN mdl_user ON mdl_user.id = mdl_role_assignments.userid 
WHERE mdl_role.id = 3 

回报这样的事情，以每门课程并作为其分配给老师的表。

COURSE_ID TEACHER 
2   john 
3   mary 
4   john 

现在，我的第二个SQL是这样的：

SELECT mdl_feedback.course, AVG(mdl_feedback_value.value) as average 
FROM mdl_feedback_value 
INNER JOIN mdl_feedback_item ON mdl_feedback_value.item = mdl_feedback_item.id 
INNER JOIN mdl_feedback ON mdl_feedback.id = mdl_feedback_item.feedback 
INNER JOIN mdl_feedback_completed ON mdl_feedback.id = mdl_feedback_completed.feedback 
INNER JOIN mdl_user ON mdl_feedback_completed.userid = mdl_user.id 
GROUP BY mdl_feedback.course 

COURSE AVERAGE 
2   3.5 
3   3 
4   3.25 

我想对那些2个SQL查询作为重点

合并成一个是这样的，当然使用/ COURSE_ID

TEACHER AVERAGE 
john   3,375 <--- avg of 3,5 and 3,25 from each of john's courses 
mary   3  <--- she has just one course so no math here 

我不知道如何去做这件事，所以我很感激一点帮助:)正如我所说，我有一段时间没有使用SQL，所以我并不热衷于这些JOIN事情，也许我必须像在这里使用它们一样使用它们。

我正在使用MySQL 5.5.33，尽管这与Moodle有关，但答案并非真正以Moodle为中心，因为这里唯一重要的是两个查询的输出是什么表。

感谢

Answer 1

如果你把每个子查询，然后尝试加入他们的行列，它应该工作。我添加了第三个字段，以帮助您查看创建乐谱的详细信息。

SELECT username, AVG(average) AS average 
    , GROUP_CONCAT(CONCAT('Course: ', teachers.course_id,' with score ', COALESCE(average,'No Score Found'))) AS detail 
FROM (
    SELECT mdl_course.id AS course_id, mdl_user.username AS username 
    FROM mdl_course 
    INNER JOIN mdl_context ON mdl_context.instanceid = mdl_course.id 
    INNER JOIN mdl_role_assignments ON mdl_context.id = mdl_role_assignments.contextid 
    INNER JOIN mdl_role ON mdl_role.id = mdl_role_assignments.roleid 
    INNER JOIN mdl_user ON mdl_user.id = mdl_role_assignments.userid 
    WHERE mdl_role.id = 3) AS teachers 
LEFT JOIN (
    SELECT mdl_feedback.course AS course_id, AVG(mdl_feedback_value.value) as average 
    FROM mdl_feedback_value 
    INNER JOIN mdl_feedback_item ON mdl_feedback_value.item = mdl_feedback_item.id 
    INNER JOIN mdl_feedback ON mdl_feedback.id = mdl_feedback_item.feedback 
    INNER JOIN mdl_feedback_completed ON mdl_feedback.id = mdl_feedback_completed.feedback 
    INNER JOIN mdl_user ON mdl_feedback_completed.userid = mdl_user.id 
    GROUP BY mdl_feedback.course) AS scores 
    ON teachers.course_id = scores.course_id 
GROUP BY username 

Answer 2

我想使用一个临时表来存储两个不同的查询结果集，然后后，我查询临时表中得到老师的平均值。希望这可以工作。

CREATE TABLE #TEMP 
(
COURSE_ID int, 
TEACHER varchar(100), 
COURSE int, 
AVERAGE int 
) 
--- Inserting the course_id and Teahcer data---- 

INSERT INTO #TEMP 
(
COURSE_ID, 
TEACHER 
) 
SELECT mdl_course.id, mdl_user.username FROM mdl_course 
INNER JOIN mdl_context ON mdl_context.instanceid = mdl_course.id 
INNER JOIN mdl_role_assignments ON mdl_context.id = mdl_role_assignments.contextid 
INNER JOIN mdl_role ON mdl_role.id = mdl_role_assignments.roleid 
INNER JOIN mdl_user ON mdl_user.id = mdl_role_assignments.userid 
WHERE mdl_role.id = 3 

-- Inserting the course and average data--- 
INSERT INTO #TEMP 
(
COURSE, 
AVERAGE 
) 
SELECT mdl_feedback.course, AVG(mdl_feedback_value.value) as average 
FROM mdl_feedback_value 
INNER JOIN mdl_feedback_item ON mdl_feedback_value.item = mdl_feedback_item.id 
INNER JOIN mdl_feedback ON mdl_feedback.id = mdl_feedback_item.feedback 
INNER JOIN mdl_feedback_completed ON mdl_feedback.id = mdl_feedback_completed.feedback 
INNER JOIN mdl_user ON mdl_feedback_completed.userid = mdl_user.id 
GROUP BY mdl_feedback.course 


--- Querying the # temp table for the average and teacher--- 

SELECT TEACHER, AVG(AVERAGE) 
FROM #TEMP 
GROUP BY TEACHER 

Answer 3

你可以尝试使用

INNER JOIN mdl_course ON mdl_feedback.course = mdl_course.id 

请看看这个组合查询工作连接两个疑问：

SELECT mdl_user.username, AVG(mdl_feedback_value.value) as average 
FROM mdl_feedback_value 
INNER JOIN mdl_feedback_item ON mdl_feedback_value.item = mdl_feedback_item.id 
INNER JOIN mdl_feedback ON mdl_feedback.id = mdl_feedback_item.feedback 
INNER JOIN mdl_feedback_completed ON mdl_feedback.id = mdl_feedback_completed.feedback 
INNER JOIN mdl_user ON mdl_feedback_completed.userid = mdl_user.id 
INNER JOIN mdl_course ON mdl_feedback.course = mdl_course.id 
INNER JOIN mdl_context ON mdl_context.instanceid = mdl_course.id 
INNER JOIN mdl_role_assignments ON mdl_context.id = mdl_role_assignments.contextid 
INNER JOIN mdl_role ON mdl_role.id = mdl_role_assignments.roleid 
INNER JOIN mdl_user ON mdl_user.id = mdl_role_assignments.userid 
WHERE mdl_role.id = 3 
GROUP BY mdl_user.username;