Question

我在MySQL中有三个表：application，questions和questions_answer。

application存储user_id; questions存储question_id和type of questions（即姓名，身份证，学校名称）; questions_answer存储引用answers和user_id的{{1}}。

据我所知，这种类型的关联称为多态关联。现在我迷失了如何从不同的question_id中检索数据并将它们作为列标题。

我希望这是有道理的。

编辑：

为了说明，以下是各自的表格：

question_id：

application

user_id name ------------------------------- 100 Leon Barnacles 101 Richard Kennard 102 Fareeza Salleh：

questions

question_id question_name --------------------------------------------- 20 NRIC 21 Have you ever applied to TFM? 22 What's your current GPA? 23 Name of school：

questions_answer

我希望检索：

question_id     user_id     answer
------------------------------------------------
20              100         880808-06-8990
20              100         900990-14-0911
23              102         SMK Taman Pandamaran

Answer 1

您需要的是PIVOT类型函数，MYSQL不支持SQL Server或Oracle等PIVOT。您可以使用以下脚本在问题表数据

上使用pivot来实现max and case

select group_concat(concat('max(case when question_id = ''', question_id, ''' then
             answer end) as `', question_name ,'`')) into @sql from tfm_questions;

set @sql = 
concat('select full_name, ', @sql, ' from 
          (
             select a.full_name, q.question_name, an.answer, q.question_id
             from tfm_application a
             inner join tfm_questions_answer an on a.user_id = an.user_id
             inner join tfm_questions q on an.question_id = q.question_id
          ) x
       group by full_name');


select @sql;

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

SQL DEMO

如何从多态MySQL表中检索数据

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