儘管數據庫中沒有任何內容，MySQL仍保留返回行，即使數據庫中沒有任何內容與查詢匹配

$ query_check_homework保持失敗。我相信這可能是一個非常簡單的東西，就像語法錯誤，但我一直在這工作了一個多小時，並且無法工作。你可以看看代碼，讓我知道爲什麼它會一直返回一行，即使數據庫中沒有任何內容與查詢匹配。儘管數據庫中沒有任何內容，MySQL仍保留返回行，即使數據庫中沒有任何內容與查詢匹配

這是代碼。

/*Check if homework name already exists*/ 
$query_check_homework = $this->db_connection->query(" 
SELECT 
    homework.homework_name 
FROM classes 
    INNER JOIN homework On classes.class_id = homework.class_id 
WHERE 
    homework.class_id = '".$this->class_id."' And 
homework.homework_name = '".$this->homework_name."' And 
classes.user_id = '".$this->user_id."'");  

if ($query_check_homework == 1) { 
    $this->errors[] = "Sorry, You already have homework in this class with that name. Please choose a different name."; 
} 
else { 
    /*write new homework into the datebase*/ 
    $query_new_homework = $this->db_connection->query(" 
    INSERT INTO homework (class_id, homework_name, avaliable_points, earned_points,  date) VALUES ('".$this->class_id."', '".$this->homework_name."', '".$this- >avaliable_points."', '".$this->earned_points."', '".$this->homework_date."')");

來源

2013-05-28 user2363217