如何使用mysqli关键字连接数据库

Question

我是PHP新手，请关注this tutorial将php webservices连接到android下面是我的代码我将MySQL更改为MySQLi，但仍显示错误：

    <?php
$host="localhost"; //replace with database hostname 
$username="root"; //replace with database username 
$password=""; //replace with database password 
$db_name="emp_info"; //replace with database name

$con=mysqli_connect("$host", "$username", "$password")or die("cannot  
  connect"); 
mysqli_select_db("$db_name")or die("cannot select DB");
$sql = "select * from emp_info"; 
$result = mysqli_query($sql);
$json = array();

if(mysqli_num_rows($result)){
while($row=mysqli_fetch_assoc($result)){
$json['emp_info'][]=$row;
}
}
mysqli_close($con);
echo json_encode($json); 
 ?> 

Answer 1

有两种解决方案，首先使用mysqli_connect()中的第四个参数。

像这样：

$con=mysqli_connect($host, $username, $password, $db_name)

其次，您需要在mysqli_select_db()

中传递连接

$con=mysqli_connect($host, $username, $password);
mysqli_select_db($con, $db_name);

MySQLi中的几乎所有函数都需要第一个参数的连接，所以mysqli_query()也需要连接。

$con=mysqli_connect($host, $username, $password, $db_name)or die("cannot connect"); 

$sql = "select * from emp_info"; 
$result = mysqli_query($con, $sql); //<--- here query need the connection