Question

Please help me with an issue that I have come across during work. I’m working with SQL Server, and I’m aware that using cursors I could achieve this, but I’m pretty sure that there is a way of doing it using simple query in SQL, but my brain bulb doesn’t want to turn on. Let me explain my issue with an example.

I have got a table like this:

postedby    |   date        |   comment |
1           |   01.01.2012  |   sth sth |
2           |   01.01.2012  |   sth sth |
3           |   01.01.2012  |   sth sth |
2           |   01.01.2012  |   sth sth |
3           |   02.01.2012  |   sth sth |
2           |   03.01.2012  |   sth sth |
2           |   05.01.2012  |   sth sth |

What I want to accomplish is get all the posts but one for every user (postedby column), the date must be the latest and of course show the comment.

I have tried doing:

Select distinct postedby, date, comment

but didn’t work, as I understand distinct works for every column, so if in 2 rows postedby is the same but comment is different it will treat it as distincts

I have tried doing:

Select postedby,date,comment group by postedby (don’t bother about the from clause)
giving me the error or aggregation, so I tried
select postedby,min(date) group by postedby – of course works, but I can’t get the comment.

Should I use in some way aggregated queries? Or what am I missing?

Answer 1

Looks like today is the RowNumber function day!!
If all you needed is the latest date and comment for each post:

SELECT postedBy, date, comment
FROM (SELECT ROW_NUMBER() OVER (PARTITION BY postedby, ORDER BY date DESC) AS RowNumber, 
             postedBy, date, comment
      FROM MyTable) t 
WHERE RowNumber = 1