sql select from table then compare with other table in one statement - php

Question

I have to tables in one database.
users
user_activate
I have to variables in php
$username = foo;
$key = jas823k123ksd34324;
Now I want to select from the table users the attribute user_id where user_username == $username
I do this with this statement
$sql = "SELECT user_id FROM users WHERE user_username = '$username'";
$result = mysqli_query($db, $sql);
while($row = mysqli_fetch_assoc($result)){
$user_id = $row['user_id'];
}
Now I want to select from the table user_activate the attribute user_activate_key where user_activate_key == $key;
For this I use this statement:
$sql2 = "SELECT user_activate_key FROM user_activate WHERE user_activate_key = '$key'";
$result2 = mysqli_query($db, $sql2);
while($row = mysqli_fetch_assoc($result)){
$user_key = row['user_activate_key'];
}
Can I do both statements in one statement?

Answer 1

As you've written it, two seperate queries is the correct way to do it. But I suspect that there's some kind of relationship between users and user_activate that might make what you're asking for make sense. Assuming that a user_activate_key is tied to a specific user_id, you could do something like the following:
select users.user_id, ua.user_activate_key
from users u
left join user_activate ua
on u.user_id = ua.user_id
and ua.user_activate_key = '$key'
where u.username = '$username'
The LEFT JOIN means that the user will be shown even if there isn't a matching user_activate_key record.