SQL - 不同类别的列

SQL - columns for different categories(SQL - 不同类别的列)

问题描述

我是 SQL 新手.我有一个包含不同考试数据的数据库，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，我想打印一份使用测试(T1、T2 和 T3)作为列的报告:

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，但我一直不知道如何生成这样的打印输出.任何帮助表示赞赏！

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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