Question

I have 2 tables, one containing information on a city (in a game) and another containing scores as recorded throughout periods of the day. Table examples have been simplified.

CREATE TABLE cities(
  cid INT(100),
  name VARCHAR(100),
  updatedAt DATETIME
);
CREATE TABLE cl_scores(
  cid INT(100),
  score INT(255),
  updatedAt DATETIME
);

I’m trying to gather a list of scores for a particular city. The list should only contain the MAX(updatedAt) date and score for every day. Here is what I have so far:

SELECT a.cid, b.name, a.score, a.updatedAt FROM ci_scores AS a 
JOIN cities AS b ON a.cid = b.cid 
JOIN (SELECT MAX(updatedAt) AS maxUpdatedAt FROM ci_scores 
GROUP BY DATE(updatedAt)) AS L ON DATE(L.maxUpdatedAt) = DATE(a.updatedAt) 
WHERE a.cid = 10158241 ORDER BY a.updatedAt ASC;

However, it isn’t returning a single entry for each day. It is in fact returning every row in the ci_scores table and simply adding the name field as shown below:

+----------+---------+-------+---------------------+
| cid      | name    | score | updatedAt           |
+----------+---------+-------+---------------------+
| 10158241 | Genesis |  3087 | 2012-03-13 04:04:03 |
| 10158241 | Genesis |  3207 | 2012-03-13 17:48:56 |
| 10158241 | Genesis |  3255 | 2012-03-14 00:44:11 |
| 10158241 | Genesis |  3262 | 2012-03-14 10:21:05 |
| 10158241 | Genesis |  3262 | 2012-03-14 13:42:42 |
+----------+---------+-------+---------------------+

What am I doing wrong in my query???

Solutions Tried

SELECT a.cid, b.name, a.score, a.updatedAt FROM ci_scores AS a 
JOIN cities AS b ON a.cid = b.cid 
JOIN (SELECT MAX(updatedAt) AS maxUpdatedAt FROM ci_scores 
GROUP BY DATE(updatedAt) LIMIT 1) AS L ON L.maxUpdatedAt = a.updatedAt
WHERE a.cid = 10158241 ORDER BY a.updatedAt ASC;

This did not work, removing the DATE() = DATE() makes it return 0 records as the times are different. If I add that back in it returns:

+----------+---------+-------+---------------------+
| cid      | name    | score | updatedAt           |
+----------+---------+-------+---------------------+
| 10158241 | Genesis |  3087 | 2012-03-13 04:04:03 |
| 10158241 | Genesis |  3207 | 2012-03-13 17:48:56 |
+----------+---------+-------+---------------------+

This is not correct, I need 1 record for each day and that record being the latest entered on that day.

Answer 1

I think you should join your subset by updateAT without DATE function

SELECT a.cid, b.name, a.score, a.updatedAt FROM ci_scores AS a 
JOIN cities AS b ON a.cid = b.cid 
JOIN (SELECT MAX(updatedAt) AS maxUpdatedAt FROM ci_scores 
GROUP BY DATE(updatedAt)) AS L ON L.maxUpdatedAt = a.updatedAt
WHERE a.cid = 10158241 ORDER BY a.updatedAt ASC;

UPDATE:
There is another error that in the sub query you need to group by the city id as well so that you can get the correct max date:

SELECT a.cid, b.name, a.score, a.updatedAt FROM ci_scores AS a 
JOIN cities AS b ON a.cid = b.cid 
JOIN (SELECT MAX(updatedAt), cid AS maxUpdatedAt FROM ci_scores 
GROUP BY DATE(updatedAt), cid) AS L ON L.maxUpdatedAt = a.updatedAt AND L.cid = a.cid
WHERE a.cid = 10158241 ORDER BY a.updatedAt ASC;