Question

I have the following situation:

In a table I have 4 columns:

CommentsTBL:
ID int
Data datetime
Hour Varchar
Comment Varchar

The Hour column is of varchar type, don’t ask me why….

Given a specific date and hour from the table, I need to find the previous and the next record. If I will find one of them (previous or next) it will be simple to get the other one using the same logic.

As an example:

ID  Data        Hour    Comment
1.  2011-01-12  17:00   SomeComments1
2.  2011-01-14  10:00   SomeComments3
3.  2011-01-14  11:00   SomeComments4
4.  2011-01-13  14:00   SomeComments2

The previous date for ID 4 would be ID 1 and the next one will be ID 2.

I came up with a solution for this, but I want to see if any of you have something better, maybe using just one SELECT. This is for the previous one:

SELECT 
       Data,
       MAX(Hour) Hour
FROM 
       CommentsTBL
WHERE 
       Data in (SELECT 
                      MAX(Data) 
                FROM 
                      CommentsTBL
                WHERE 
                      Data < MyDate or (Data = MyDate and Hour < MyHour)
               )
GROUP BY
         Data

Thanks.

Answer 1

Why not:

select *
  from ( SELECT data, hour from commentsTbl
          where data < mydate
             or ( data = mydate and hour < myhour )
          order by data desc, hour desc
          limit 1 
       )
 union all
select *
  from ( SELECT data, hour from commentsTbl
          where data > mydate
             or ( data = mydate and hour > myhour )
          order by data asc, hour asc
          limit 1
       )