Filter LEFT JOINed table with dates to display current event, else future, else past? - sql

Question

I have a table that lists vacation information for different users (username, vacation start, and vacation end dates) -- 4 users are listed below:
Username VacationStart DeploymentEnd
rsuarez 2014-03-10 2014-03-26
studd 2014-01-18 2014-01-29
studd 2014-02-11 2014-02-26
studd 2014-03-02 2014-03-04
ssteele 2014-03-11 2014-03-26
ssteele 2014-03-18 2014-03-28
atidball 2014-03-05 2014-03-20
atidball 2014-03-06 2014-03-26
atidball 2014-03-13 2014-03-20
atidball 2014-03-18 2014-03-31
For a new query, I want to display only 4 rows, with each user having only one set of vacation dates displayed, either current/in-progress vacation, future/next vacation (if no current exists) or most recent (if two above are false).
The end result should be following (assuming today is 3/9/2014):
Username VacationStart DeploymentEnd
rsuarez 2014-03-10 2014-03-26
studd 2014-03-02 2014-03-04
ssteele 2014-03-11 2014-03-26
atidball 2014-03-05 2014-03-20
Vacation dates are actually coming from another table (data_vacations), which I left join to data_users. I am trying to perform case selection inside left join statement.
Here is what I tried before, but my logic fails there, since I ended up to mix different vacation end dates to vacation start dates:
SELECT Username, VacationStart, VacationEnd
FROM data_users
LEFT JOIN
(
SELECT userGUID,
CASE WHEN MIN(CASE WHEN (VacationEnd < getdate()) THEN NULL ELSE VacationStart END) IS NULL THEN MAX(VacationStart)
ELSE MIN(VacationStart) END AS VacationStart,
CASE WHEN MIN(CASE WHEN (VacationEnd < getdate()) THEN NULL ELSE VacationEnd END) IS NULL THEN MAX(VacationEnd)
ELSE MIN(VacationEnd) END AS VacationEnd
FROM data_vacations
GROUP BY userGUID
) b ON(data_empl_master.userGUID= b.userGUID)
What am I doing wrong? How could I fix it?
Also.. on side note.. Do I perform this filtering in LEFT JOIN correctly? Since data_users is much bigger, having distinct user ids... and I would like to join the available vacation information based on example above, while still displaying all unique user ids.

Answer 1

Using a common table expression to rank by category (current = 1, future = 2, past = 3) and each category individually by start date/differene from GETDATE(), you can get the result you want by ranking the result using ROW_NUMBER();
DECLARE #DATE DATETIME = GETDATE()
;WITH cte AS (
SELECT *, 1 r, VacationStart s FROM data_users
WHERE #DATE BETWEEN VacationStart and DeploymentEnd
UNION ALL
SELECT *,2 r, VacationStart - #DATE s FROM data_users
WHERE VacationStart > #DATE
UNION ALL
SELECT *,3 r, #DATE - DeploymentEnd s FROM data_users
WHERE DeploymentEnd < #DATE
), cte2 AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY username ORDER BY r,s) rn FROM cte
)
SELECT Username, VacationStart, DeploymentEnd FROM cte2 WHERE rn=1;
An SQLfiddle to test with.
Getting the date as a variable is necessary to get a consistent GETDATE() value over the whole query, otherwise it may not be consistent if called multiple times.

Answer 2

select u.name,s.startdate,s.enddate
from users u
left join
(
select su.name,
max(su.start) as startdate,
max(su.end) as enddate from users su group by su.name
)s on u.name= s.name
group by u.name

Answer 3

Since you are asking two questions I will answer the one about getting the vacation dates and let you figure out the join.
I don't think you can get the desired vacations dates in one simple query. First you need to establish if the given date range is in past, present or future. Then you need to order those ranges by start/end dates to get the most recent or next upcoming. You need sort the past vacations in descending and upcoming in ascending order. Funny enough user atidball has two vacations in-progress, I sorted that in the same manner as future vacation. Finally apply your rules, I did that by sorting by state.
declare #currentDate date = '20140309'
;
with cte1 as
(
-- state: the lower number the higher priority
select Username, VacationStart, DeploymentEnd,
case
when VacationStart <= #currentDate and DeploymentEnd >= #currentDate
then 0 -- in progress
when VacationStart > #currentDate
then 1 -- future
when DeploymentEnd < #currentDate
then 2 -- past
else NULL
end as state
from data_vacations
)
, cte2 as
(
select *,
row_number() over(partition by username, state order by VacationStart, DeploymentEnd) as rn
from cte1
where state < 2 -- current or upcoming
union all
select *,
row_number() over(partition by username, state order by DeploymentEnd desc, VacationStart desc) as rn
from cte1
where state = 2 -- past
)
, cte3 as
(
-- apply the rules: find the record with highest priority
select Username, min(state) as minstate
from cte1
group by Username
)
select cte2.Username, cte2.VacationStart, cte2.DeploymentEnd
from cte2
inner join cte3
on cte2.Username = cte3.Username
and cte2.state = cte3.minstate
and cte2.rn = 1 -- most recent or next upcoming
See the SQLFiddle.