Combine MySQL SELECT queries with IF statement - php

Question

I want to combine my two SELECT statements with an if statement. Currently I am just getting the row and then doing if($row['activated'] === 1) { ... run 2nd select statement }.
There has to be a better and much faster way of doing it (performance-wise). This is what I'm trying to do:
For example: (1st SELECT statement)
$db = $stmt->("SELECT * FROM users WHERE id = :id AND activated = 1");
$db->bindParam(':id', $id);
$db->execute();
If that above SELECT statement is true, then do this: (2nd SELECT statement)
$db = $stmt->("SELECT * FROM user_settings WHERE user_id = :user_id");
$db->bindParam(':user_id', $id);
$db->execute();
How can I combine those two SELECT statements? If it is else or if activated = 0, then only do the first select.
Bonus question:
How can I make it three If statements? For example, the 2nd SELECT statement will be like this:
$db = $stmt->("SELECT * FROM user_settings WHERE user_id = :user_id AND color = :color");
$db->bindParam(':user_id', $id);
$db->bindParam(':color', $color);
$db->execute();
Now if that statement is true, run this 3rd SELECT statement:
$db = $stmt->("SELECT * FROM friends WHERE user_id = :user_id");
$db->bindParam(':user_id', $id);
$db->execute();

Answer 1

You can merge/combine
SELECT * FROM user_settings WHERE user_id = :user_id AND color = :color
and
SELECT * FROM friends WHERE user_id = :user_id
Into one query with a JOIN
SELECT
*
FROM
user_settings
INNER JOIN
friends
ON
user_settings.user_id = friends.user_id
AND
user_settings.color = :color
Or a other JOIN format
SELECT
*
FROM
user_settings
INNER JOIN
friends
ON
user_settings.user_id = friends.user_id
WHERE
user_settings.color = :color
Or you can write it as this JOIN. (most likely slower)
SELECT
*
FROM (
SELECT
*
FROM
user_settings
WHERE
user_settings.color = :color
) AS user_settings
INNER JOIN
friends
ON
user_settings.user_id = friends.user_id
The used method which is best/faster can/will be depending which indexes you have in use.