PHP Mysqli错误：mysqli_query（）期望参数1为mysqli，给定布尔值

Question

this is not a question, I need your help. I read similar threads but I couldn't debug the problem in my code. Could you plz give the correct solution?

<?php
/*variable declaration*/
$host="localhost";
$user="root";
$pass="";
$dbname='mydatabase';

/*connection to mysql server*/
$connect = mysqli_connect($host,$user,$pass);

/*selecting database*/
$selectdb=mysqli_select_db($connect,$dbname);

if(!$selectdb){
    echo 'Failed to connect. Wrong username or database.';
}else{
    echo 'Connection successful.';
}

/*creating task*/
$query = "SELECT 'Name', 'Password' FROM 'db' ORDER BY 'id'";

if(mysqli_query($selectdb,$query)){
echo 'Success';
}else{
echo '<br>Failed';
}
?>

enter image description here

Answer 1

Modify

$query = "SELECT 'Name', 'Password' FROM 'db' ORDER BY 'id'";

To

$query = "SELECT `Name`, `Password` FROM db ORDER BY 'id'";

You just cannot use the quotes on column name on the query, either use backticks or nothing at all.

Answer 2

if(mysqli_query($connect,$query)){...

在这种情况下，您需要使用$connect而不是$selectdb 。

Answer 3

<?php
/*variable declaration*/
$host="localhost";
$user="root";
$pass="";
$dbname='mydatabase';
$connect = mysqli_connect($host,$user,$pass,$dbname);

/*I avoided this line & used $connect inside if() statement which worked    perfectly*/
//$selectdb = mysqli_select_db($connect,$dbname);

if(!$connect){
    echo 'Failed to connect. Wrong username or database.';
}else{
    echo 'Connection successful.';
}

/*creating task*/
$query = "SELECT `Name`, `Password` FROM `db` ORDER BY `id`";

if($query_run = mysqli_query($connect,$query)){
echo 'Success';
}else{
echo '<br> Failed';
}