如何使用mysqli的關鍵字

Question

連接數據庫我在PHP新，採用this tutorial連接PHP Web服務下面以Android是我的代碼更改MySQL到MySQLi無處不在，但它仍然顯示錯誤：

<?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

有兩種解決方法，首先使用mysqli_connect()中的第四個參數。

像這樣：

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

其次，你需要傳遞mysqli_select_db()

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

連接幾乎在所有的MySQLi函數所需的連接如在第一個參數，所以mysqli_query()需要的連接了。

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

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