mysqli查询返回true但fetch_assoc不起作用

Question

I am using PHP and MySQL (mysqli) in XAMPP, I have a drop down, and the user must choose one, then a query is used to find the id of the value that has been chosen but it does not work. I have already done this three more times and it worked but this one doesn't.

    $sql = "SELECT foo_id FROM foo_table
WHERE foo_name = 'bar';";
    $res = $conn->query($sql);
    for ($i = 0; $i < 500; $i++) {
        $row = $res->fetch_assoc();
        echo $row[row["foo_id"]]
    }

The problem is that fetch_assoc does not return anything even though the $res variable returns true.

Edit: I forgot to mention that running the query in phpmyadmin returns results normally.

Answer 1

I am not sure why you are iterating over 500 times? this doesn't make sense.

Best practice to retrieve the data from DB is

$sql  = "SELECT foo_id FROM foo_table
          WHERE foo_name = 'bar'";
$res = $conn->query($sql);
if ($res->num_rows > 0) {
   // output data of each row
   while($row = $res->fetch_assoc()) {
      echo $row["foo_id"];
   }
 }

OR

 $foo_id = ''
 if ($res->num_rows > 0) {
   // output data of each row
   while($row = $res->fetch_assoc()) {
      $foo_id = $row["foo_id"];
   }
 }
 for ($i = 0; $i < 500; $i++) {
    echo $foo_id;
 }

Answer 2

我找到了解决方案，问题是真实的数据库在记录中使用了希腊字符而数据库必须设置为utf8-bin，这样做之后才有效。