Join 如何将一个mysql数据库中的2列与另一个数据库中的4列连接起来

我有2个mysql数据库。（1） authorID，authorFirst，authorLast。（2） courseID，courseName，courseAuthor1，courseAuthor2，courseAuthor3，courseAuthor4。如何将authors数据库中的2个列连接到courses数据库中的一个或全部4个courseAuthor列

作者

authorID | authorFirst | authorLast
1        |   firstA    |   lastA   
2        |   firstB    |   lastB 
3        |   firstC    |   lastC 
4        |   firstD    |   lastC 

课程

courseID | courseName | courseAuthor1 | courseAuthor2 | courseAuthor3 | courseAuthor4
1        | course1    |      2        |     3         |    NULL       |     NULL
2        | course 2   |      1        |     4         |     3         |     NULL
3        | course 33  |      4        |     1         |     2         |     NULL
4        | course 4   |      3        |    NULL       |    NULL       |     NULL

我希望结果如下所示：

courseID | courseName | courseAuthor1 | courseAuthor2 | courseAuthor3 | courseAuthor4
1        | course1    | firstB LastB  | firstC LastC  |     NULL      |     NULL
2        | course 2   | firstA LastA  | firstD LastD  | firstC LastC  |     NULL
3        | course 33  | firstD LastD  | firstA LastA  | firstB LastB  |     NULL
4        | course 4   | firstC LastC  |    NULL       |    NULL       |     NULL

我甚至不知道从哪里开始。这是我的密码：

从课程中选择*在authors.authorID中加入作者 （courses.courseAuthor1，courses.courseAuthor2，courses.courseAuthor3， 课程。课程（4）

这表明：

results  |  courseID | courseName | courseAuthor1 | courseAuthor2 | courseAuthor3 | courseAuthor4  |  authorID  |  authorFirst  |  authorLast
1        |    1      | course1    |      2        |     3         |    NULL       |     NULL       |      2     |     firstB    |  lastB
2        |    1      | course1    |      2        |     3         |    NULL       |     NULL       |      3     |     firstC    |  lastC
3        |    2      | course 2   |      1        |     4         |     3         |     NULL       |      1     |     firstA    |  lastA
4        |    2      | course 2   |      1        |     4         |     3         |     NULL       |      4     |     firstD    |  lastD
5        |    2      | course 2   |      1        |     4         |     3         |     NULL       |      3     |     firstC    |  lastC
6        |    3      | course 33  |      4        |     1         |     2         |     NULL       |      4     |     firstD    |  lastD
7        |    3      | course 33  |      4        |     1         |     2         |     NULL       |      1     |     firstA    |  lastA
8        |    3      | course 33  |      4        |     1         |     2         |     NULL       |      2     |     firstB    |  lastB
9        |    4      | course 4   |      3        |    NULL       |    NULL       |     NULL       |      3     |     firstC    |  lastC

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非常感谢

我花了一些时间，但我已经回答了我的问题。这是：

SELECT c1.courseID, c1.courseName, 
CONCAT(a1.authorFirst,' ',a1.authorLast) AS aOne, 
CONCAT(a2.authorFirst,' ',a2.authorLast) AS aTwo, 
CONCAT(a3.authorFirst,' ',a3.authorLast) AS aThree, 
CONCAT(a4.authorFirst,' ',a4.authorLast) AS aFour 
FROM courses c1 
LEFT JOIN authors a1 ON c1.courseAuthor1 = a1.authorID 
LEFT JOIN authors a2 ON c1.courseAuthor2 = a2.authorID 
LEFT JOIN authors a3 ON c1.courseAuthor3 = a3.authorID 
LEFT JOIN authors a4 ON c1.courseAuthor4 = a4.authorID