Question

Select t.Name, a.Questions, b.Correct,c.Attempted from Topics t 
Left Join (
SELECT  COUNT(TestResults2.QuestionID) AS Questions, 
Topics.Name
FROM TestResults INNER JOIN
TestResults2 ON TestResults.ID = TestResults2.TestResultID 
INNER JOIN QuestionBank ON TestResults2.QuestionID = QuestionBank.ID 
INNER JOIN Topics ON QuestionBank.TopicID = Topics.ID
WHERE TestResults.StudentID = 1
AND TestResults.ID = 46
GROUP BY Topics.Name) a 
On t.Name=a.Name
Inner Join (
SELECT COUNT(TestResults2.QuestionID) AS Correct, 
Topics.Name
FROM TestResults INNER JOIN
TestResults2 ON TestResults.ID = TestResults2.TestResultID 
INNER JOIN QuestionBank ON TestResults2.QuestionID = QuestionBank.ID 
AND TestResults2.Answer = QuestionBank.Answer 
INNER JOIN Topics ON QuestionBank.TopicID = Topics.ID
WHERE TestResults.StudentID = 1
AND TestResults.ID = 46
GROUP BY Topics.Name) b 
On t.Name=b.Name
Inner Join (
SELECT COUNT(TestResults2.QuestionID) AS Attempted, 
Topics.Name
FROM  TestResults INNER JOIN
TestResults2 ON TestResults.ID = TestResults2.TestResultID 
INNER JOIN QuestionBank ON TestResults2.QuestionID = QuestionBank.ID 
AND TestResults2.Answer <> '\0' 
INNER JOIN Topics ON QuestionBank.TopicID = Topics.ID
WHERE TestResults.StudentID = 1
AND TestResults.ID = 46
GROUP BY Topics.Name) c 
on c.Name=t.Name

Answer 1

SELECT      t.Name, a.Questions, b.Correct,c.Attempted 
FROM        Topics t 
LEFT JOIN   (
            SELECT  COUNT(TestResults2.QuestionID) AS Questions, 
                    Topics.Name
            FROM    TestResults 
            JOIN    TestResults2 ON TestResults.ID = TestResults2.TestResultID 
            JOIN    QuestionBank ON TestResults2.QuestionID = QuestionBank.ID 
            JOIN    Topics ON QuestionBank.TopicID = Topics.ID
            WHERE   TestResults.StudentID = 1
            AND     TestResults.ID = 46
            GROUP   BY Topics.Name) a On t.Name=a.Name
LEFT JOIN       (
            SELECT  COUNT(TestResults2.QuestionID) AS Correct, 
                    Topics.Name
            FROM    TestResults 
            JOIN    TestResults2 ON TestResults.ID = TestResults2.TestResultID 
            JOIN    QuestionBank ON TestResults2.QuestionID = QuestionBank.ID AND TestResults2.Answer = QuestionBank.Answer 
            JOIN    Topics ON QuestionBank.TopicID = Topics.ID
            WHERE   TestResults.StudentID = 1
            AND     TestResults.ID = 46
            GROUP   BY Topics.Name) b On t.Name=b.Name
LEFT JOIN       (
            SELECT  COUNT(TestResults2.QuestionID) AS Attempted, 
                    Topics.Name
            FROM    TestResults 
            JOIN    TestResults2 ON TestResults.ID = TestResults2.TestResultID 
            JOIN    QuestionBank ON TestResults2.QuestionID = QuestionBank.ID AND TestResults2.Answer <> '\0' 
            JOIN    Topics ON QuestionBank.TopicID = Topics.ID
            WHERE   TestResults.StudentID = 1 
            AND     TestResults.ID = 46
            GROUP   BY Topics.Name) c on c.Name=t.Name

这是你的查询，我只是用LEFT JOIN更改了一些JOINS，检查你是否能够处理NULL值。

如何处理具有空值的连接脚本（无数据）

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