结合MySQL SELECT查询和IF语句

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.