mysqli_select_db（）错误，数据库无法连接

Question

您好我是PHP的新手，我编写了一个php页面并创建了一个数据库。我试图连接数据库，但它没有连接。

<?php
$uname = "root";
$pwd = "";
$hostn = "localhost"; 

//connection to the database
$mysqlconn = mysqli_connect($hostn, $uname, $pwd)
  or die("Unable to connect to MySQL");

//select a database to work with
$dbselect = mysqli_select_db("dataforuse",$mysqlconn)
  or die("Could not select dataforuse");
mysql_close($mysqlconn);
?>

Answer 1

您正在混合使用mysql和mysqli

你必须替换

/connection to the database
$mysqlconn = mysqli_connect($hostn, $uname, $pwd)
  or die("Unable to connect to MySQL");

//select a database to work with
$dbselect = mysqli_select_db("dataforuse",$mysqlconn)
  or die("Could not select dataforuse");

使用此代码

$mysqlconn = mysqli_connect($hostn, $uname, $pwd,"dataforuse")
  or die("Unable to connect to MySQL");

Answer 2

嗨尝试调试和回应与mysqli_error() function相关的错误。

    $uname = "root";
    $pwd = "";
    $hostn = "localhost"; 

    //connection to the database

        $mysqlconn = mysqli_connect($hostn, $uname, $pwd) or die(mysqli_connect_error());

or 

      $mysqlconn = mysqli_connect($hostn, $uname, $pwd , $database) or die(mysqli_connect_error());

Answer 3

连接变量然后数据库名称..这个

$dbselect = mysqli_select_db($mysqlconn,"dataforuse");

和mysql关闭应该是这样的

   mysqli_close($mysqlconn);

不要将mysql与mysqli混合

Answer 4

你应该写

<?php
$uname = "root";
$pwd = "";
$hostn = "localhost";
$dbname = "dataforuse";

$conn = new mysqli($hostn, $uname, $pwd, $dbname);
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

?> 

这将解决您的问题