注意：未定义索引：第 13 行 C:\wamp64\www\quiz\remove\repeated.php 中的 Ans

Question

如何解决？

注意：未定义索引：Ans in C:\wamp64\www\quiz\remove\repeated.php 第 13 行

我的代码：

require_once '../class.user.php';
$user_home = new USER();
$lstmtf = $user_home->runQuery("SELECT COUNT(Ans)
FROM answer AS a
LEFT JOIN students_records AS s ON a.Sr = s.Sr
WHERE s.Sr IS NULL");
    $lstmtf->execute();
$reg_rst = $lstmtf->fetch(PDO::FETCH_ASSOC);
$registered= $reg_rst['Ans'];
        echo $registered;

我的表answer有列名Ans。

其实我想统计students_records中没有值的行数。

例如：

students_records

+----+-----+-----+ 
| Sr | SRN | ARN |
+----+-----+-----+
| 1  | ge  | aj  |
| 2  | ge  | bd  |
+----+-----+-----+  

回答

+----+-----+-----+
| Sr | SRN | ARN |
+----+-----+-----+
| 1  | ge  | aj  |
| 2  | ge  | aj  |
| 3  | ge  | ne  |
| 4  | ge  | bd  |
+----+-----+-----+ 

这里的计数应该是 1。由于表答案的列ARN 中的值“ne”在students_records 表中ARN 列的行中没有。

Answer 1

这样使用

$lstmtf = $user_home->runQuery("SELECT COUNT(Ans) as Ans
FROM answer AS a
LEFT JOIN students_records AS s ON a.Sr = s.Sr
WHERE s.Sr IS NULL");

Answer 2

你可以通过关注得到愿望输出

SELECT count(a.Ans) as ans
FROM answer AS a
LEFT JOIN students_records AS s ON a.ARN = s.ARN
WHERE   s.ARN IS NULL

这里正在工作example