Question

我正在尝试在数据库中创建一个表。数据库test存在，我收到错误No database selected。我相信我使用代码$select_db = mysql_select_db($database);

选择了数据库

以下是代码：

$host_name = 'localhost';
$user_name = 'root';
$password  = '';
$database = "test";
$connection = mysqli_connect($host_name,$user_name,$password);
$select_db = mysql_select_db($database);
if ($select_db) {

    echo "Database found <br>";
    # code...
}
else
{
    echo "Database not found <br>";
}


//code Working correctly till DATABASE FOUND.

$sql = "CREATE TABLE employee (employee_id INT(4) NOT NULL PRIMARY KEY AUTO_INCREMENT , Name CHAR(30) NOT NULL)";

if (mysqli_query($connection,$sql)) 
{
    # code...
    echo "Table created successfully";
}

else
{
    echo "Table not created with the following error<br><strong>".mysqli_error($connection)."</strong>";
}

/*$db_close = mysql_close($Connection);
if ($db_close) {

    echo "Connection closed";

    # code...
}

else
{
    echo "Connection not closed";
}*/

?>

Answer 1

$connection = mysqli_connect($host_name,$user_name,$password);

VS

$select_db = mysql_select_db($database);

看起来非常接近:)找到一个 i ，这会让一切变得与众不同。

找到错误后，请再次访问 mysqli_connect 文档，了解如何为其提供数据库名称。用1块石头杀死2只鸟。

Answer 2

您正在混合mysql和mysqli个扩展程序。不推荐使用mysql。仅使用mysqli或PDO。

// mysqli here
$connection = mysqli_connect($host_name,$user_name,$password);
// and mysql here
$select_db = mysql_select_db($database);

更改为

 $select_db = mysqli_select_db($database);

Answer 3

您实际上只是检查$select_db是否为空。

在数据库连接上运行查询之前，您必须连接到它。

这是我一直在使用的示例课程。

<?php
    class database{

        // Database settings
        protected $_mysqli = false;
        protected $_db     = array(
            "username" => "username here",
            "password" => "password here",
            "host"     => "localhost",
            "database" => "database name here",
            "charset"  => "utf8"
        );

        // Function to connect to the database
        function connect() {
            $mysqli = new mysqli($this->_db['host'], $this->_db['username'], $this->_db['password'], $this->_db['database']);
            if ( $mysqli->connect_errno ) {
                $this->_mysqli = false;
            }else {
                $mysqli->set_charset($this->_db['charset']);
                $this->_mysqli = $mysqli;
            }
        }

        // Function to execute an sql query
        function execute_query($sql) {
            if ( $results = $this->_mysqli->query($sql) ) {
                return $results;
            }else {
                return false;
            }
        }
    }
?>

您可以连接到数据库并运行如下所示的查询：

<?php
    //Includes the class file
    require_once('database.php');
    // Connects to the database
    $database_connection = new database();
    // To execute a sql query
    $query_response = $database_connection->execute_query("SELECT * FROM table");
?>

但是你实际上从未连接到你的数据库。

错误：未在php中选择数据库

3 个答案: