Nested queries - is there a smarter way

Question

I have a question about nested/subqueries that's been bugging me for a while now.

I'm programming a game in php. In a very simple version of my system I have the following 3 tables:

players (each player only has one entry):

| player_id | player_name |

stats (each player has one entry for each game he is in):

| stat_id | player_id | game_id | outcome |

games (each games has one entry):

| game_id | game_name |

I would like to query my database and have a table with rows structured like the following to be the output:

| player_name | count stats for player where outcome = 1 || count stats for player where outcome = 2 |

I have the following which works, but i think there's a smarter and better way of doing it:

select a.player_name,
    (select count(*) from stats b where b.player_id = a.player_id AND b.outcome = 1) as number_of_games1,
    (select count(*) from stats b where b.player_id = a.player_id AND b.outcome = 2) as number_of_games2 
from players a

I would also like to be able to use "number_of_games1" or "number_of_games2" in the outer where, but the above approach doesn't allow for this:

select a.player_name,
    (select count(*) from stats b where b.player_id = a.player_id AND b.outcome = 1) as number_of_games1,
    (select count(*) from stats b where b.player_id = a.player_id AND b.outcome = 2) as number_of_games2 
from players a where number_of_games > 5

What is the smartest way of doing what i want to do?

Thanks.

Answer 1

You can make use of SUM() function with a condition and use a join,Using SUM() with condition will result in a boolean 1 or 0 so you can count your desired results for b.outcome = 1 and b.outcome = 2

SELECT 
a.player_id,
a.player_name,
SUM(b.outcome = 1) as number_of_games1,
SUM(b.outcome = 2) as number_of_games2 
FROM players a 
LEFT JOIN stats b ON(b.player_id = a.player_id)
GROUP BY a.player_id
HAVING number_of_games1 > 5 
/* you can add second condition for number_of_games2 
starting with any conditional operator  
*/