注意：未定义的索引：第13行的C：\ wamp64 \ www \ quiz emove epeated.php中的Ans
问题描述：
How to resolve this?
Notice: Undefined index: Ans in C:\wamp64\www\quizemoveepeated.php on line 13
My code:
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;
My table answer has column name Ans.
Actually, I want to count the numbers of rows which do not have values in students_records.
For Eg:
students_records
+----+-----+-----+
| Sr | SRN | ARN |
+----+-----+-----+
| 1 | ge | aj |
| 2 | ge | bd |
+----+-----+-----+
answer
+----+-----+-----+
| Sr | SRN | ARN |
+----+-----+-----+
| 1 | ge | aj |
| 2 | ge | aj |
| 3 | ge | ne |
| 4 | ge | bd |
+----+-----+-----+
Here count should be 1. As the value "ne" in column ARN of table answer is no where in the rows of column ARN in table students_records.
答
You can get the desire output by following
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
Here is working example
答
Use like this
$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");