SELECT * FROM multiple column - php

Question

I am absolute beginner in creating database and
I only know that we can use,
"SELECT * FROM users WHERE username = '$username' and password = '$password'";
but, what if there is multiple table in my SQL and I want to select them all?
can I just do,
"Select * from users where username = '$username' and password = '$password' and email = '$email' and address = '$address' and phone = '$phone'";
Here are my PHP script:
public function does_user_exist($username,$password,$email,$address,$phone){
$query = "Select * from users where username = '$username' and password = '$password' and email = '$email' and address = '$address' and phone = '$phone'";
$result = mysqli_query($this->connection, $query);
if(mysqli_num_rows($result) > 0){
$json['success'] = 'Welcome '.$email;
echo json_encode($json);
mysqli_close($this->connection);
} else {
$query = "Insert into users(username, password, email, address, phone) values ('$username','$password','$email', '$address', '$phone')";
$is_inserted = mysqli_query($this->connection, $query);
if ($is_inserted == 1){
$json['success'] = 'Account created, welcome '.$email;
} else {
$json['error'] = 'Wrong password ';
}
echo json_encode($json);
mysqli_close($this->connetion);
}
}
UPDATE
<?php
require_once 'connection.php';
header('Content-Type: application/json');
class User {
private $db;
private $connection;
function __construct() {
$this->db = new DB_Connection();
$this->connection = $this->db->get_connection();
}
public function does_user_exist($username,$password,$email,$address,$phone){
$query = ("Select * from users where username = '$username' and password = '$password' and email = '$email' and address = '$address' and phone = '$phone'");
$result = mysqli_query($this->connection, $query);
if(mysqli_num_rows($result) > 0){
$json['success'] = 'Welcome '.$email;
echo json_encode($json);
mysqli_close($this->connection);
} else {
$query = "Insert into users(username, password, email, address, phone) values ('$username','$password','$email', '$address', '$phone')";
$is_inserted = mysqli_query($this->connection, $query);
if ($is_inserted == 1){
$json['success'] = 'Account created, welcome '.$email;
} else {
$json['error'] = 'Wrong password ';
}
echo json_encode($json);
mysqli_close($this->connetion);
}
}
}
$user = new User();
if (isset($_POST['username'], $_POST['password'], $_POST['email'], $_POST['address'], $_POSt['phone'])){
$username = $POST['username'];
$password = $_POST['password'];
$email = $_POST['email'];
$address = $_POST['address'];
$phone = $_POST['phone'];
if(!empty($username) && !empty($password) && !empty($email) && !empty($address) && !empty($phone)){
$encrypted_password = md5($password);
$user -> does_user_exist($username,$encrypted_password,$email,$address,$phone);
} else {
echo json_encode("You must fill all fields!")
}
}
?>
Hopefully you guys can help, I really appreciate the answers.

Answer 1

You have to use JOIN Queries. Try the below SQL Statement
SELECT table1.column1, table2.column2...
FROM table1
INNER JOIN table2
ON table1.common_field = table2.common_field;
Refer this JOIN SQL SO Answers
What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN?
Difference in MySQL JOIN vs LEFT JOIN
Mysql join query

Answer 2

Generally speaking you will want to use JOIN to do this, and you will need to have values in common between your tables, which act as foreign keys, referencing corresponding values in other tables.
EDIT
Updates to the question and comments indicate that the original question was slightly misphrased. Yes, you can absolutely reference/use/compare/evaluate numerous columns in a single query. The example you posted is a good example:
SELECT (column1, column2) FROM users WHERE username = $username AND email = $email
And so on, for as many columns as the table has. You can also use the OR operator, which has the effect of including any row that matches on username OR on email (or whatever other columns you like).