I have a notification table as follows
|id|user_receiver|user_sender|post_id|action|date|is_read
here user_sender
is the person who generated notification, user_receiver
is one who got the notification, post_id
is id of post, action
can be like, comment etc, is_read
is 1 if its read by receiver else 0
I want to get all notifications for loggedin user
query that I am using is
SELECT id, user_receiver, user_sender, post_id, action,
max(date) as date, is_read
FROM notification
WHERE user_receiver=$ses_user
group by user_sender, action,post_id,is_read
order by date desc
but it doesn't give me latest rows even though I am using max(date)
and I also want to get number of notifications that are unread.
I want only one row if there are multiple rows having same post_id, user_sender and action together and that should be the latest one. For example a user likes a post, a row is added to the table, then user dislikes and likes again, then a new row is added again, I want only the new row only.
To get the latest row in MySQL, you need to use a join
or correlated subquery:
SELECT id, user_receiver, user_sender, post_id, action, date, is_read
FROM notification n
WHERE user_receiver=$ses_user and
date = (select max(date)
from notification n2
where n2.user_sender = n.user_sender and
n2.action = n.action and
n2.post_id = n.post_id and
n2.is_read = n.is_read
)
order by date desc;
In other databases, you would simply use the row_number()
function (or distinct on
in Postgres).
EDIT:
For the biggest id:
SELECT id, user_receiver, user_sender, post_id, action, date, is_read
FROM notification n
WHERE user_receiver=$ses_user and
id = (select max(id)
from notification n2
where n2.user_sender = n.user_sender and
n2.action = n.action and
n2.post_id = n.post_id
)
order by date desc;
If you want the number of rows where isread = 1
, then you can do something like:
SELECT sum(is_read = 1)
FROM notification n
WHERE user_receiver=$ses_user and
id = (select max(id)
from notification n2
where n2.user_sender = n.user_sender and
n2.action = n.action and
n2.post_id = n.post_id
);