Select last record out of grouped records - sql

Question

i have this code and i want someone to help me to change it to a grouped query which orders froms below.
SELECT *
FROM dbo.users_pics INNER JOIN profile
ON users_pics.email = profile.email
Left Join photo_comment
On users_pics.u_pic_id = photo_comment.pic_id
WHERE users_pics.wardrobe = MMColParam
ORDER BY u_pic_id asc
what i mean is i have grouped of records which i want to select one per record only from beneath. for example if i have 10 records of the name "John" i want to select the last "John" out of the 10 and then the rest also follows

Answer 1

I'm going to presume that your users table contains a single user, and each user has a single profile, and your photo_comment table can contain multiple comments.
Depending on your RDBMS, you can do this a number of ways. Row_Number can often be a quick way of doing this if you're using a database which supports window functions such as SQL Server or Oracle.
A generic solution to this is to join the table back to itself using the MAX aggregate. This is dependent on having a field to determine which record is the max. Generally speaking, that would be an identity/auto number field or a time stamp field.
Here is the basic concept using photo_comment_id as your determining column:
SELECT *
FROM dbo.users_pics INNER JOIN profile
ON users_pics.email = profile.email
LEFT Join (
SELECT pic_id, MAX(photo_comment_id) max_photo_comment_id
FROM max_photo_comment
GROUP BY pic_id
) max_photo_comment On users_pics.u_pic_id = max_photo_comment.pic_id
LEFT Join photo_comment On
max_photo_comment.pic_id = photo_comment.pic_id AND
max_photo_comment.max_photo_comment_id = photo_comment.photo_comment_id
WHERE users_pics.wardrobe = MMColParam
ORDER BY u_pic_id asc
If your database supports ROW_NUMBER, then you can do this as well (still using the photo_comment_id field):
SELECT *
FROM (
SELECT *,
ROW_NUMBER() OVER (PARTITION BY photo_comment.pic_id
ORDER BY photo_comment.photo_comment_id DESC) rn
FROM dbo.users_pics INNER JOIN profile
ON users_pics.email = profile.email
LEFT JOIN photo_comment
ON users_pics.u_pic_id = photo_comment.pic_id
WHERE users_pics.wardrobe = MMColParam
) t
WHERE rn = 1
ORDER BY u_pic_id asc