PHP：连接到数据库，但mysql_query失败

Question

I have very strange problem with PHP which I am starting to learn .. I have created tables in MySQL database with some data, and now I want to show them in webpage.

This is my source where I have this problem:

<?php
    // Here I open connection
    $con = mysql_connect("localhost","root","aaaaaa");
    // set the mysql database
    $db = mysql_select_db("infs", $con);

    // I check the connection
    if (mysqli_connect_errno())
    {
        echo "Failed to connect to MySQL: " . mysqli_connect_error();
    }
    else {
        // It always goes here
        echo "Connected to database!";
    }

    // I am testing very simple SQL query.. there should be no problem
    $result = mysql_query("SELECT * FROM cathegories", $con, $db);

    if (!$result) {
        // but it always dies
        $message  = 'Invalid query: ' . mysql_error() . "\n";
        $message .= 'Whole query: ' . $query;
        die($message);
    }

    mysql_close($con);
?>

What is wrong?

Thanks in advance!

Answer 1

// Here I open connection
$con = mysql_connect("localhost","root","aaaaaa");
// set the mysql database
$db = mysql_select_db("infs", $connection);

change to

// Here I open connection
$con = mysql_connect("localhost","root","aaaaaa");
// set the mysql database
$db = mysql_select_db("infs", $con);

Answer 2

You are mixing mysql and mysqli. Try something like:

<?php   
    $con= new mysqli("localhost","user","passwd","database");
    if ($con->connect_errno){
      echo "could not connect";
    }

    $select = "SELECT * FROM tablename";

    if($result = $con->query($select)){
        while($row = $result->fetch_object()){
            echo $row->rowname."<br>";
        }
    }
    else { echo 'no result'; }
    $con->close();  
?>

Answer 3

mysql_query only takes two parameters - the actual SQL and then the link identifier (I assume in your case that's stored in $con; therefore remove $db from the third parameter).

You don't even need the second $con parameter really.

Where's the actual logic to connect to the database initially? Just because mysqli_connect_errno() doesn't return an error it doesn't mean the connection actually exists and that $con is available in the current scope.

I'd var_dump($con) before the mysql query to make sure it's a valid connection.