Question

Here’s a real noobish MySQL query problem I’m having.

I have a high score table in a game I’m writing. The high score DB records a name, level, and score achieved. There are many near duplicates in the db. For example:

Name | Level | Score | Timestamp (key) Bob    2       41    | 1234567.890 Bob    3       15    | 1234568.890 Bob    3       20    | 1234569.890 Joe    2       40    | 1234561.890 Bob    3       21    | 1234562.890 Bob    3       21    | 1234563.890 

I want to return a ‘highest level achieved’ high score list, with an output similar to:

Name | Level | Score Bob    3       21 Joe    2       40 

The SQL Query I currently use is:

SELECT *, MAX(level) as level  FROM highscores  GROUP BY name ORDER BY level DESC, score DESC LIMIT 5 

However this doesn’t quite work. The ‘Score’ field output always seems to be randomly pulled from the group, instead of taking the corresponding score for the highest level achieved. Eg:

Name | Level | Score Bob    3       41 Joe    2       40 

Bob never got 41 points on level 3! How can I fix this?

Answer 1

You’ll need to use a subquery to pull the score out.

select distinct     name,      max(level) as level,     (select max(score) from highscores h2          where h2.name = h1.name and h2.level = h1.level) as score from highscores h1  group by name  order by level desc, score desc 

Cheers,

Eric

It irks me that I didn’t take the time to explain why this is the case when I posted the answer, so here goes:

When you pull back everything (*), and then the max level, what you’ll get is each record sequentially, plus a column with the max level on it. Note that you’re not grouping by score (which would have given you Bob 2 41, and Bob 3 21–two records for our friend Bob).

So, how the heck do we fix this? You need to do a subquery to additionally filter your results, which is what that (select max(score)…) is. Now, for each row that reads Bob, you will get his max level (3), and his max score at that level (21). But, this still gives us however many rows Bob has (e.g.-if he has 5 rows, you’ll get 5 rows of Bob 3 21). To limit this to only the top score, we need to use a DISTINCT clause in the select statement to only return unique rows.

UPDATE: Correct SQL (can’t comment on le dorfier’s post):

SELECT h1.Name, h1.Level, MAX(h1.Score)     FROM highscores h1     LEFT OUTER JOIN highscores h2 ON h1.name = h2.name AND h1.level < h2.level     LEFT OUTER JOIN highscores h3 ON h1.name = h3.name AND h2.level = h3.level AND h1.score < h3.score     WHERE h2.Name IS NULL AND h3.Name IS NULL     GROUP BY h1.Name, h1.Level