Question

I have a test database which logs data from when a store logs onto a store portal and how long it stays logged on.

Example:
(just for visualizing purposes – not actual database)

Stores
Id  Description     Address         City
 1  Candy shop      43 Oxford Str.  London
 2  Icecream shop   45 Side Lane    Huddersfield

Connections
Id  Store_Ref   Start                    End
 1          2   2011-02-11 09:12:34.123  2011-02-11 09:12:34.123
 2          2   2011-02-11 09:12:36.123  2011-02-11 09:14:58.125
 3          1   2011-02-14 08:42:10.855  2011-02-14 08:42:10.855
 4          1   2011-02-14 08:42:12.345  2011-02-14 08:50:45.987
 5          1   2011-02-15 08:35:19.345  2011-02-15 08:38:20.123
 6          2   2011-02-19 09:08:55.555  2011-02-19 09:12:46.789

I need to get various data from the database. I’ve already gotten the max and average connection duration. (So probably very self-evident that..) I also need to have some information about which connection lasted the least. I ofcourse immediately thought of the Min() function of Linq, but as you can see, the database also includes connections that started and ended instantly. Therefore, that data isn’t actually “valid” for data analysis.

So my question is how to get the minimum value, but if the value = 0, get the next value that is the lowest.

My linq query so far (which implements the Min() function):

var min = from connections in Connections
          join stores in Stores
             on connections.Store_Ref equals stores.Id
          group connections
             by stores.Description into groupedStores
          select new
          {
             Store_Description = groupedStores.Key,
             Connection_Duration = groupedStores.Min(connections => 
                                             (SqlMethods.DateDiffSecond(connections.Start, connections.End)))
          };

I know that it’s possible to get the valid values through multiple queries and/or statements though, but I was wondering if it’s possible to do it all in just one query, since my program expects linq queries to be returned and my preference goes to keeping the program as “light” as possible.

If you have to great/simple method to do so, please share it. Your contribution is very appreciated! 🙂

Answer 1

var min = from connections in Connections.Where(connections => (SqlMethods.DateDiffSecond(connections.Start, connections.End) > 0)
          join stores in Stores
             on connections.Store_Ref equals stores.Id
          group connections
             by stores.Description into groupedStores
          select new
          {
             Store_Description = groupedStores.Key,
             Connection_Duration = groupedStores.Min(connections => 
                                             (SqlMethods.DateDiffSecond(connections.Start, connections.End)))
          };

Try this, With filtering the “0” values you will get the right result, at least that is my taught.