Haven't heard back, so I thought I'd provide my updated solution:

create table #Channels (

ChannelDate datetime,

SourceId int,

ChannelId int,

Value varchar(128));

insert into #Channels

values

('2015-11-01 16:45:59.953',1,1,'223,4923'),

('2015-11-01 16:46:00.127',1,2,'224,9357'), --*

('2015-11-01 16:46:00.327',1,3,'227,4183'), --*

('2015-11-01 16:46:00.527',1,4,'221,025'), --*

('2015-11-01 13:17:14.177',1,1,'223,0304'), --*

('2015-11-02 14:34:16.337',1,1,'223,1234'),

('2015-12-01 16:45:59.953',1,1,'323,4923'),

('2015-12-01 16:46:00.127',1,2,'324,9357'), --*

('2015-12-01 16:46:00.327',1,3,'327,4183'), --*

('2015-12-01 16:46:00.527',1,4,'321,025'), --*

('2015-12-01 13:17:14.177',1,1,'323,0304'); --*

with basedata as (

select

ChannelDate,

SourceId,

ChannelId,

Value,

rn = row_number() over (partition by ChannelId,dateadd(month,datediff(month,0,ChannelDate),0) order by ChannelDate asc)

from

#Channels

where

ChannelDate >= dateadd(month,datediff(month,0,ChannelDate),0) and ChannelDate < dateadd(month,datediff(month,0,ChannelDate),1)

)

select

ChannelDate,

SourceId,

ChannelId,

Value

from

basedata

where

rn = 1

order by

ChannelDate, ChannelId;