SQL - 检索过去7天的最后一天记录

Question

I am inserting a record every hour into my table. Now I need to retrieve the most recent record of each day for the last 30 days.

Here is my table:

pl_scores: {
  score_id: 'BIGINT(255) PRIMARY KEY AUTO_INCREMENT'
, pid: 'INT(100)'
, score: 'INT(255)'
, rank: 'INT(50)'
, city_cnt: 'INT(10)'
, updatedAt: 'DATETIME'
}

Since there is 24 records for each day I am at a loss as to how to pull the most recent only for that day. Any help would be appreciated.

Answer 1

Step 1 - Break them into groups by day.
Step 2 - Select the timestamp of the last entry for each group.
Step 3 - Go back and get the records that match those timestamps.

SELECT
  pl_scores.*
FROM
  pl_scores
INNER JOIN
  (SELECT MAX(updatedAt) AS maxUpdatedAt FROM pl_scores GROUP BY DATE(updatedAt)) as Lookup
    ON Lookup.MaxUpdatedAt = pl_scores.updatedAt

Note: This assumes that each record has a different value in updatedAt. If they're not unique, and multiple records are tied for being the most recent on any given day, all the tied records are returned.