PHP 试图获取非对象的属性

Question

$sql = "select customer-name, customer-city from customer where customer-name in (select distinct customer-name from depositor, account where depositor.account-number=account.account-number and account.branch-name='Downtown')";
$result = $conn->query($sql);
if ($result->num_rows > 0) { //LINE 18
  // output result in each row
  while($row = $result->fetch_assoc()) {
    echo "Name: ". $row['customer-name']. " " . $row["customer-city"] . "<br>";
  }
} else {
  echo "0 results";
}

The error I get:

PHP Notice:  Trying to get property of non-object in line 18

I tried using an array and that did not work either, I got the same error.

Answer 1

In the PDO call of query ( https://www.php.net/manual/en/pdo.query.php ), you can see the following: PDO::query() returns a PDOStatement object, or false on failure.

It means that if the query fails, you keep only a false instead of the PDOStatement object.

$sql = "select customer-name, customer-city from customer where customer-name in (select distinct customer-name from depositor, account where depositor.account-number=account.account-number and account.branch-name='Downtown')";
$result = $conn->query($sql);
if ($result == false) {
  echo "Query failed";
} else if ($result->num_rows > 0) {
  // output result in each row
  while($row = $result->fetch_assoc()) {
    echo "Name: ". $row['customer-name']. " " . $row["customer-city"] . "<br>";
  }
} else {
  echo "0 results";
}