PDO提取结果或在while循环中使用布尔值

Question

I'm trying to output a HTML form with nil values if there are no records in the database. However, if there are records (there could be multiple sets of data), I want to default the values in the form to what's already in the records.

So I have a PDO query and fetch set up as follows:

$con = new PDO(...);
$con->setAttribute(...);
$query = "SELECT DISTINCT data FROM ...";
$stmt = $con->prepare($query);
$stmt->execute();
$first_loop = true; //print 1 form if data set is empty
while ($first_loop || $obj = $stmt->fetch()) {
    //process $obj and print form
    $first_loop = false;
}

The issue with the above code is that $stmt->fetch() does not point to the next row after processing one set of data. If I remove $first_loop from the while statement then everything works fine, only if there is at least one set of data in my records. Because if there isn't, my entire form doesn't get printed.

I'm not sure if the above method is the best to achieve my objective, but if it is, I'd like to hear how I can improve my code to solve the bug.

Thanks!

Answer 1

You can check for no of rows, and if its greater than zero, it means database contains values.
Use num_rows

$stmt = $con->prepare($query);
$stmt->execute();
$stmt->store_result();
if($stmt->num_rows>0) {  // database contains values
    while ($obj = $stmt->fetch()) {
        //process $obj and print form

    }
}
else{  // form must have null values because no data found on database

}

Answer 2

You can't check your condition in while loop.Instead you can use if and isset to check your condition

$first_loop = true; //print 1 form if data set is empty. 

    if(isset($first_loop))
    while ($obj = $stmt->fetch()) {
        //process $obj and print form
        $first_loop = false;
    }
    }else{
    $first_loop = false;
    }

Answer 3

 $servername = "localhost"; $username = "user"; $password = "pass"; $dbname = "test"; $conn = new mysqli($servername, $username, $password, $dbname); if ($conn->connect_error) { die("Connection failed: " . $conn->connect_error); } $sql = "SELECT DISTINCT data FROM ..."; $result = $conn->query($sql); if ($result->num_rows > 0) { while($row = $result->fetch_assoc()) { echo $row["data"]."<br>"; } } else { echo nil; } $conn->close();