Question

I want to create an SQL Query for a SQLite3 DB.

In my table I have the following sample data

7/1/2011   8:00   LOGIN
7/1/2011   10:12  LOGOFF
7/1/2011   10:20  LOGIN
7/1/2011   17:15  LOGOFF
7/2/2011   9:00   LOGIN
7/3/2011   10:00  LOGIN
7/3/2011   20:00  LOGOFF

basically I want to only get the first LOGIN entry per date and the last LOGOFF entry for the same date (if available)

So I want the query to produce

7/1/2011   8:00   LOGIN
7/1/2011   17:15  LOGOFF
7/2/2011   9:00   LOGIN
7/3/2011   10:00  LOGIN
7/3/2011   20:00  LOGOFF

Is is also possible to calculate the difference in Time with the desired output table?

IE/ on 7/1/2011 would be 9:15

Answer 1

Supposing your columns are named Date, Time, Action, this is what you need:

select Date,
       case Action 
         when 'LOGIN' then Min(Time)
         when 'LOGOFF' then Max(Time)
       end as ActionTime,
       Action 
from YourTable
group by Date, Action

Update

For calculating the difference, you might want to “flatten” the rows of a day to a single row:

select Date, MinLoginTime, MaxLogoffTime, MaxLogoffTime - MinLoginTime as Diff
from
(
select Date,
       Min(
           case Action 
               when 'LOGIN' then Time
               else null
           end
       ) as MinLoginTime,
       Max(
           case Action 
               when 'LOGOFF' then Time
               else null
           end
       ) as MaxLogoffTime
from YourTable
group by Date
) YourDT

Some considerations:

• If you don’t have MinLoginTime OR MaxLogoffTime, Diff will be null
• You will probably have to work on formatting Diff. Do some research on that for SQLite, every RDBMS has its particularities on that matter.