SQL-不同类别的列 [英] SQL - columns for different categories

问题描述

我是SQL新手.我有一个数据库，其中包含用于不同考试的数据，例如:

I am new to SQL. I have a database with data for different exams, for example:

Student Test Grade
--------------------
St1    T1   A
St2    T1   B
St3    T1   B
St1    T2   B
St2    T2   B
St3    T2   A
St1    T3   A
St2    T3   C
St3    T3   B

然后，我想使用测试"(T1，T2和T3)作为列来打印报告:

Then, I would like to print a report using the Tests (T1, T2 and T3) as columns:

Student  T1   T2   T3
----------------------
St1      A    B    A
St2      B    B    C
St3      B    A    B

我尝试了不同的方法，但是我对如何产生这样的打印输出卡住了.感谢您的帮助！

I have tried different things, but I got stuck on how to produce such a printout. Any help is appreciated!

推荐答案

使用:

  SELECT t.student,
         MAX(CASE WHEN t.test = 'T1' THEN t.grade END) AS T1,
         MAX(CASE WHEN t.test = 'T2' THEN t.grade END) AS T2,
         MAX(CASE WHEN t.test = 'T3' THEN t.grade END) AS T3
    FROM TABLE t
GROUP BY t.student

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