Question

I am trying to learn php and mysql. So i tried making a database using phpmyadmin and connect it with my php. Here is a simple example where I try to see if the database is working

<?php
$connection = mysql_connect("localhost","root");
if(!$connection) {
    die("Database connection failed: " . mysql_error());
    $db_select = mysql_select_db("nameofdatabase",$connection);
    if (!$db_select) {
        die("Database selection failed:: " . mysql_error());
        }
    }
?>
<html>
<head>
<title>Databases</title>
</head>
<body>
<?php
$result = mysql_query("SELECT * FROM nameofdatabasetable", $connection);
if (!$result) {
    die("Database query failed::: " . mysql_error());
}
while ($row = mysql_fetch_array($result)) {
echo $row[1];
}

?>

</body>
  </html>
<?php
mysql_close($connection);
?>

并且我得到

 Database query failed::: No database selected

代码的此部分

<?php
$result = mysql_query("SELECT * FROM users", $connection);
if (!$result) {
    die("Database query failed::: " . mysql_error());
}
while ($row = mysql_fetch_array($result)) {
echo $row[1];
}

?>

is not working (i put a different number of these ":" in each if. Any help would be appreciated! Thank you!

Answer 1

您的代码逻辑不合理, 因为如果连接不发生, 那么您将无法选择数据库, 如果您无法连接到数据库, 您的数据库选择的语句在逻辑范围内。请尝试 :

$connection = mysql_connect("localhost","root"); 
if(!$connection) { 
   die("Database connection failed: " . mysql_error()); 
}else{
   $db_select = mysql_select_db("nameofdatabase",$connection); 
   if (!$db_select) { 
       die("Database selection failed:: " . mysql_error()); 
   } 
}

Answer 2

我要在 Mysql_ connect call 中通过用户名和密码。这是我的数据库打开() 功能。

    $this->con_error = "";

    $db_con= mysql_connect($this->server, $this->username, $this->password);

    if (!$db_con) 
    {
        $this->con_error = mysql_error();
        return false;
    }       
    if(!mysql_select_db($this->database))
    {
        $this->con_error = mysql_error();
        return false;
    }

    return $db_con;

Answer 3

die("Database connection failed: " . mysql_error());
$db_select = mysql_select_db("nameofdatabase",$connection);

mysql_select_db 无法在此运行。它只在死后调用。

$connection = mysql_connect("localhost","root");
if(!$connection) {
  die("Database connection failed: " . mysql_error());
}
$db_select = mysql_select_db("nameofdatabase",$connection);
if (!$db_select) {
  die("Database selection failed:: " . mysql_error());
}

Answer 4

Also it would be worth checking if you entered a password to your server. $connection = mysql_connect("localhost","root"); (Missing Password)

以下代码将捕捉可能发生的任何其他错误, 就像下面的答案一样, 这将提供 Mysql 的连接错误, 以防出现任何错误。

    try 
   {
        $connection = mysql_connect("localhost","root", "password");
        if(!$connection) {   
          die("Database connection failed: " . mysql_error());   
        }   
        $db_select = mysql_select_db("nameofdatabase",$connection);   
        if (!$db_select) {   
          die("Database selection failed:: " . mysql_error());   
         }   

   }catch (Exception $e){
       error_log(" DB Error: ".$e->getMessage());
   }

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