MySQL:将同一个表中具有不同列名的多个 WHERE 子句组合在一起

Question

我是 MySQL 新手，正在通过 PluralSight 学习。我正在尝试执行一个查询，结果为 4 列。 4 列中的 3 列来自同一列，但通过指向数值的 WHERE 子句进行区分。此外，我还包括来自不同表的一列。我觉得修复很容易，但正如我提到的，我对此很陌生。单独来看，这些部分工作得很好，但我不知道如何正确地加入它们。任何帮助，将不胜感激。迄今为止我的工作包含在下面。

Select answer as FirstName
FROM glpi.glpi_plugin_formcreator_answers
WHERE plugin_formcreator_questions_id = 1

Select answer as MI
FROM glpi.glpi_plugin_formcreator_answers
WHERE plugin_formcreator_questions_id = 54 

Select answer as LastName
FROM glpi.glpi_plugin_formcreator_answers
WHERE plugin_formcreator_questions_id = 55

Select request_date
FROM glpi.glpi_plugin_formcreator_forms_answers

Answer 1

这不是答案

因为我怀疑您在需求中遗漏了一些重要的内容

我只想为您提供一种您想要获得的方法，您唯一缺少的是GROUP BY列。

SELECT
   IF(plugin_formcreator_questions_id = 1,answer, null) as FirstName
   IF(plugin_formcreator_questions_id = 54,answer, null) as MI,
   IF(plugin_formcreator_questions_id = 55,answer, null) as LastName,
   request_date
FROM glpi.glpi_plugin_formcreator_answers
WHERE plugin_formcreator_questions_id IN (1,54,55)

所以最终版本应该是这样的:

SELECT
   form_id,
   MAX(IF(plugin_formcreator_questions_id = 1,answer, null)) as FirstName
   MAX(IF(plugin_formcreator_questions_id = 54,answer, null)) as MI,
   MAX(IF(plugin_formcreator_questions_id = 55,answer, null)) as LastName,
   MAX(request_date)
FROM glpi.glpi_plugin_formcreator_answers
WHERE plugin_formcreator_questions_id IN (1,54,55)
GROUP BY form_id