Question

I’ve got a table in SQL 2008 that looks like this:

DECLARE @DataTable TABLE
(
    Name varchar(10),
    [TimeStamp] DateTime,
    Event varchar(10),
    Data varchar(10)
)

INSERT INTO @DataTable
VALUES  ('TEST01', '2012/03/06 10:00', 'EventA', 1),
        ('TEST01', '2012/03/06 10:01', 'EventB', 2),
        ('TEST01', '2012/03/06 11:00', 'EventC', 0)

How would I do the following in SQL:

If DataTable contains row where Name = @NewName and Event = @NewEvent Then
    If TimeStamp of the above row < @NewTimeStamp
        Update that row with new TimeStamp and Data
    EndIf
Else
    Insert row into table
EndIf

For example, I’ve got the following three data points and their expected actions:

('TEST01', '2012/03/06 10:01', 'EventA', 5), -- This should update the existing row because it's a newer EventA
('TEST01', '2011/01/01 9:00', 'EventB', 2), -- This should be discarded because a newer EventB data point exists in the table
('TEST01', '2011/05/12 17:00', 'EventD', 0), -- This should be inserted because no row in the table contains EventD

Answer 1

merge @DataTable as dt
using (select @data as data, @event as event, @name as name, @timestamp as timestamp) source 
on dt.name=source.name and dt.event=source.event
when matched and dt.timestamp <= source.timestamp then
  update
  set timestamp = source.timestamp, data = source.data
when matched and dt.timestamp > source.timestamp then 
  insert(data, event, name, timestamp)
  values(data, event, name, timestamp)
when not matched then
  insert(data, event, name, timestamp)
  values(data, event, name, timestamp)