Question

I am designing a website that people post text messages. users can rate the messages (1 to 5). I’m recording this ratings into a table to:

1. avoid multiple rating by one user for the same post
2. to be able get the average rating of a post.

but I also the number of votes are important too. for example a post having 10 votes of 3 (makes 30) are valuable than the post with 2 votes of 5 (that makes 10). Now when I’m showing a page with 20 of this messages I want to show their rating too

This is my rating table:

create table ratings(
[id] int primary key identity(1,1),
[msgid] int,
[uid] int,
[rating] tinyint
)

I want to get to 20 messages from messages table with the sum of the ratings for each message and the count of ratings for each message.

select 
    msg.id, msg.text,
    sum(rate.rating), 
    count(rate.id) 
from 
    messages as msg 
inner join 
    ratings as rate on msg.id = rate.msgid 
group by 
    msg.id

can any one please help me with the SQL query code?

Answer 1

You cannot select columns which haven’t been used in group by clause.

Try:

select 
    msg.id, msg.text,
    sum(rate.rating), 
    count(rate.id) 
from 
    messages as msg 
inner join 
    ratings as rate on msg.id = rate.msgid 
group by 
    msg.id, msg.text