Question

我有以下表格

demographic_categories

demographic_id  demographic_name
1               color
2               age_group

project_tests

test_id  group_id  project_id
1        1         1
2        1         1

test_demographic_requirements

test_id  project_id  demgraphic_id  demographic_value
1        1           1              blue
1        1           2              young
2        1           1              green
2        1           2              middle

我需要一个查询，它会给我以下结果：

test_id  group_id  color  age_group 
1        1         blue   young
2        1         green  middle

我想我们需要使用数据透视表的概念来获得结果，但我无法做到。而我的人口统计类别可能会相同，他们往往会改变，所以我需要一些动态的东西，那么最好的方法是什么呢？

我尝试过根据以前的类似问题做以下事情，但它似乎对我不起作用，这是我尝试过的：

SET @sql = NULL;
    SELECT
      GROUP_CONCAT(DISTINCT
        CONCAT(
          'max(case when dc.demographic_name = ''',
          demographic_name,
          ''' then trd.demographic_value end) AS ',
          replace(demographic_name, ' ', '')
        )
      ) INTO @sql
    from demographic_categories;

    SET @sql = CONCAT('SELECT pt.test_id, pt.group_id,
    ', @sql,'
    from test_requirement_demographic trd
    LEFT JOIN demographic_categories dc ON trd.demographic_id = dc.demographic_id
    LEFT JOIN project_tests pt ON pt.test_id = trd.test_id and project_id =1
    group by pt.test_id;');

    PREPARE stmt FROM @sql;
    EXECUTE stmt;

    DEALLOCATE PREPARE stmt;

Answer 1

除了一件事，你的动态SQL就好了。它在您的第二个左连接中有一个不明确的列project_id，只需将其替换为pt.project_id或trd.project_id，它就会得到所需的结果。

SET @sql = NULL;
    SELECT
      GROUP_CONCAT(DISTINCT
        CONCAT(
          'max(case when dc.demographic_name = ''',
          demographic_name,
          ''' then trd.demographic_value end) AS ',
          replace(demographic_name, ' ', '')
        )
      ) INTO @sql
    from demographic_categories;

SET @sql = CONCAT('SELECT pt.test_id, pt.group_id,
', @sql,'
from test_demographic_requirements trd
LEFT JOIN demographic_categories dc ON trd.demographic_id = dc.demographic_id
LEFT JOIN project_tests pt ON pt.test_id = trd.test_id and pt.project_id =1
group by pt.test_id;');

PREPARE stmt FROM @sql;
EXECUTE stmt;

DEALLOCATE PREPARE stmt;

我在rextester上运行它。这是链接：dynamic_pivot_test

动态数据透视表列mysql

1 个答案: