Question

I’m trying to create a list in PHP of the oldest entries for each user in the database.

SELECT *, 
MIN(`entries`.`entry_date`) 
AS entry_date 
FROM (`entries`) 
JOIN `user_profiles` 
ON `user_profiles`.`user_id` = `entries`.`user_id` 
WHERE `status` = 1 
GROUP BY `entries`.`user_id`

I’m using the query to retrieve from the entries table the oldest dated entry using MIN()and joining with table user_profiles for other data. The query should select the oldest entry for each user. It seems to work but it retrieves the wrong entry_date field on some entries when I echo them. Please help, I can’t spot what I’m doing wrong..

Answer 1

You need to use a subquery to obtain the (user_id, entry_date) pairs for each user, then join that with a query that selects the records of interest:

SELECT *
FROM   entries
  NATURAL JOIN (
    SELECT   user_id, MIN(entry_date) AS entry_date
    FROM     entries
    GROUP BY user_id
  ) AS tmin
  JOIN user_profiles USING (user_id)
WHERE  status = 1