Conditional logic in SQL query - mysql

Question

I have a table that looks like the following:
mysql> desc mlb_lineups;
+----------------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| player_id | int(11) | NO | MUL | NULL | |
| team_id | int(11) | NO | | NULL | |
| game_id | int(11) | NO | MUL | NULL | |
| gamedate | date | NO | | NULL | |
| pos | int(11) | NO | | NULL | |
| is_home | int(11) | NO | | 0 | |
| is_pitcher | int(11) | YES | MUL | 0 | |
| opponent_team_id | int(11) | NO | MUL | NULL | |
| first_name | varchar(255) | YES | | NULL | |
| last_name | varchar(255) | YES | | NULL | |
| position | varchar(20) | YES | | NULL | |
| hand_throws_with | varchar(1) | YES | | NULL | |
+----------------------+--------------+------+-----+---------+----------------+
In order for me to retrieve a lineup that a team used last, let's say a team with team_id 31 in this case, I'd run the following query:
select * from mlb_lineups
where team_id = 31
and pos > -1
order by gamedate DESC,
pos ASC LIMIT 9;
That works fine and dandy. What I'm trying to do though is a bit tricky and I can't seem to piece the way the inner query and/or conditional logic would work here. I want to run a query that basically says: retrieve a lineup that a team used last where the opponent_team_id had an is_pitcher equal to 1 with a hand_throws_with equal to L. mlb_lineups table will contain at least one row where a player is_pitcher is equal to 1 and hand_throws_with is equal to L where a team has a lefty throwing on the mound.
Essentially what I'd need to do to find out what the last lineup a team_id did used when their opposing pitcher had a hand_throws_with equal to L I'd have to run a query that would figure out what the last opponent_team_id they faced is with that particular handedness and then retrieve their lineup for that game_id. Does this schema provide enough information to run a single query for that? Did I provide enough information to make my problem understandable?

Answer 1

Presumably you'll need to JOIN the table back to itself using the opponent_team_id and game_id fields. There are a couple of ways to do this.
Here is one method using EXISTS:
select *
from mlb_lineups ml1
where tsn_team_id = 31
and pos > -1
and exists (
select 1
from mlb_lineups ml2
where ml1.opponent_team_id = ml2.team_id
and ml2.is_pitcher = 1
and ml2.hand_throws_with = 'L'
and ml1.game_id = ml2.game_id
)
order by gamedate desc, pos
limit 9;
This method uses a standard JOIN but it may require DISTINCT, depends on the data:
select ml1.*
from mlb_lineups ml1
inner join mlb_lineups ml2 on ml1.game_id = ml2.game_id
and ml1.team_id = ml2.opponent_team_id
and ml2.is_pitcher = 1
and ml2.hand_throws_with = 'L'
where ml1.tsn_team_id = 31
and ml1.pos > -1
order by ml1.gamedate desc, ml1.pos
limit 9;