SQL Server : max date and inner join - sql

Question

I have two tables, one is a list of tasks. The other containing historical values for those tasks.
I need to generate a list of the latest event (and its description) for each check, as long as long as its Date_Executed is less than the current datetime minus the Timeframe (TimeFrame being hours within the task has to be done, formatted for use in DATEADD). But only if they have an active = 1.
Table: checks
Check_id description TimeFrame active
1 Task One -24 0
2 Task Two -24 0
3 Task Forty -48 1
4 Task Somehin -128 1
Table: events
Event_id Check_id Comment Date_Executed User_Executed
1 1 NULL 2012-09-18 16:10:44.917 admin
2 1 NULL 2012-09-25 11:39:01.000 jeff
3 4 Failed 2012-09-25 13:20:09.930 steve
4 4 Half failed 2012-09-25 13:05:09.953 marsha
5 2 NULL 2012-09-25 14:02:24.000 marsha
6 3 NULL 2012-09-18 16:10:55.023 marsha
The best solutions I have so far is:
SELECT
a.[Date_Executed]
a.[Check_id],
a.[Comments],
b.[frequency],
b.[Check_id],
b.[description]
FROM
[checksdb].[dbo].events as a,
[checksdb].[dbo].checks as b
where
b.active = 1
and a.[Date_Executed] < = dateadd(HOUR,b.[frequency],GETDATE())
and a.Check_id = b.Check_id
order by Check_id, priority
and
select MAX(date_Executed), Task_id from daily_check_events group by Task_id
Neither of which gets me what I need, I could really use some help.

Answer 1

Since you are SQL Server which supports Common Table Expression and Window Function. Try this,
WITH latestEvents
AS
(
SELECT Event_id, Check_id, [Comment], Date_Executed, User_Executed,
ROW_NUMBER() OVER(PARTITION BY Check_ID ORDER BY DATE_Executed DESC)
AS RowNum
FROM events
)
SELECT a.[Check_id], a.[description],
b.[Date_Executed], b.[Comment]
FROM checks a
INNER JOIN latestEvents b
on a.check_ID = b.check_ID
WHERE b.RowNum = 1 AND
a.active = 1
-- other conditions here
SQLFiddle Demo
The above query will only work on RDBMS that supports Window Functions. Alternatively, use the query below that works on most RDBMS
SELECT a.Check_id, a.description,
c.Date_Executed, c.Comment
FROM checks a
INNER JOIN
(
SELECT check_id, MAX(Date_Executed) maxExecuted
FROM events
GROUP BY check_ID
) b ON a.check_ID = b.check_ID
INNER JOIN events c
ON c.check_ID = b.check_ID AND
c.date_executed = b.maxExecuted
WHERE a.active = 1
SQLFiddle Demo