如何編寫選擇查詢來獲取所有的孩子ID在父母身份在mysqli

Question

我想通過父母身份證從一個表中獲得所有的孩子ID。 下面是我的表course：

這裏是我的代碼：

public function getLeftMenuMainCategoryInfoFromDb() 
{ 
    $sqlQuery = "SELECT p.course_id AS parent_id ,p.course_name As parent_coursename ,c.course_id AS child_id ,c.course_name As child_coursename FROM course As p LEFT JOIN course As c ON c.course_parent_id = p.course_id WHERE p.course_parent_id = 0 ORDER BY p.course_id"; 
    $result = $this->selectQuery($sqlQuery); 
    //print_r($result); 
    return $result; 

} 

Answer 1

嘗試此查詢SELECT GROUP_CONCAT(course_id),course_parent_id FROM courseGROUP BY course_parent_id

SELECT GROUP_CONCAT(course_id),course_parent_id FROM course WHERE course_parent_id =1 GROUP BY course_parent_id

如果這不是你想請詳細說明您的題。

Answer 2

我想你在找父ID應該是GROUP BY

SELECT p.*, 
     q.course_name 
FROM course p 
INNER JOIN 
    (SELECT course_id, 
      course_name 
    FROM course 
    WHERE course_parent_id = 0 
    ORDER BY course_id) q ON p.course_parent_id = q.course_id 
GROUP BY p.course_parent_id;