SQL左连接外键两个表

Question

我有一个查询，我正在加入他们问题答案的表格。两个表都有一个外键，该外键链接回用户表以确定谁询问了谁以及谁回答了问题。

我的问题是，如何修改以下查询以生成product_question。userID和product_answer。userID显示来自{{1}的用户名表而不仅仅是ID？

User

Answer 1

您可以对同一个表和别名使用两个连接来区分它们：

      SELECT `project_question`.`id` AS question_id, 
             `project_question`.`question`, 
             q_user.`userName` AS askedBy, 
             `project_question`.`created` AS question_created, 
             `project_answer`.`id` AS answer_id, 
             `project_answer`.`answer`, 
             a_user.`userName` AS answeredBy, 
             `project_answer`.`accepted`, 
             `project_answer`.`created` AS answer_created
        FROM `project_question`
   LEFT JOIN `project_answer`
          ON `project_question`.`id` = `project_answer`.`questionID`
  INNER JOIN `User` AS q_user
          ON `project_question`.`userID` = q_user.`userID`
  INNER JOIN `User` AS a_user
          ON `project_answer`.`userID` = a_user.`userID`
       WHERE `project_question`.`projectID` = $args[0]
         AND `project_question`.`projectPhase` = 2