Question

userkey     keyboardkey     keypressed
----------------------------------------
u1          kb1             A
u1          kb1             B  
u1          kb2             C
u2          kb1             A
u2          kb1             B
u3          kb1             A
u3          kb1             B
u3          kb1             D  
u4          kb1             E  

How can i write a linq to sql query to get only the common keypressed.

For instance find the common keypressed where user account is in (u1, u2, u3) and keyboardkey = kb1. This will give the output as alist containing A,B.

And find the common keypressed where user account is in (u1, u2, u3, u4) and keyboardkey = kb1 then it should return nothing.

Thanks.

Answer 1

Something like this should work:

var commonKeysPressed = db.keys
                          .Where(k => userKeyList.Contains(k.userkey) 
                                 && k.keyboardkey == someKeyboardkey)
                          .GroupBy(k => k.keypressed)
                          .Where( g => g.Select( x=> x.userkey).Distinct().Count() == userCount)
                          .Select(g => g.Key)
                          .ToList();

This requires:

1. keys to be the SQL table in question
2. userKeyList to be an array of user accounts, i.e. a string array – in your example (u1, u2, u3)
3. someKeyboardkey to be some keyboard key value, in your example
   kb1.
4. userCount the number of users in the userKeyList array (userKeyList.Length)