MySQL- 通过匹配引用从多个表中获取数据

Question

我尝试使用连接查询从不同的 table 中获取数据。但是即使有数据也没有返回任何结果。

学生管理员 table 有关于学生的详细信息。学生的学号是这个 table 中的主键。在所有结果table（即first_term_results、second_term_results等）中添加卷号以供参考。

因此，为了获取学生详细信息、他的第一学期和第二学期成绩，我使用了以下查询，但未提供预期结果。我正在尝试获取与 roll_no.

匹配的详细信息

SELECT a.*, b .*,c.*
FROM student_master AS a
INNER JOIN first_term_results AS b
INNER JOIN second_term_results AS c
ON a.roll_no = b.roll_no = c.roll_no
WHERE a.roll_no = '53'
AND b.roll_no='53'
AND c.roll_no = '53'

有人可以帮助我更正此查询以获得我期望的结果吗？如果您不清楚，请告诉我。我可以解释。

提前致谢。

Answer 1

将您的查询修改为

SELECT a.*, b.*,c.*
FROM student_master AS a
INNER JOIN first_term_results AS b ON a.roll_no = b.roll_no
INNER JOIN second_term_results AS c ON a.roll_no = c.roll_no
WHERE a.roll_no = '53'

Answer 2

这应该符合您的愿望：

SELECT a.*, b .*,c.*
FROM student_master AS a
LEFT JOIN first_term_results AS b ON(a.roll_no = b.roll_no)
LEFT JOIN second_term_results AS c ON( a.roll_no = c.roll_no)
WHERE a.roll_no = '53'

你检查过驱动程序是否返回错误吗？

Answer 3

将您的查询格式化为可读的内容后，我得到了这个

SELECT a.*, b .*,c.* 
FROM   student_master AS a 
  INNER JOIN first_term_results AS b 
  INNER JOIN second_term_results AS c ON a.roll_no = b.roll_no = c.roll_no 
WHERE   a.roll_no = '53' 
AND     b.roll_no='53'
AND     c.roll_no = '53'

我觉得有点奇怪，我会选择这样的东西

SELECT a.*, b .*,c.* 
FROM   student_master AS a 
  INNER JOIN first_term_results AS b on a.roll_no = b.roll_no 
  INNER JOIN second_term_results AS c ON a.roll_no = c.roll_no 
WHERE   a.roll_no = '53'

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