Aggregating Several Columns in SQL - sql

Question

Suppose I have a table that looks like the following
id | location | dateHired | dateRehired | dateTerminated
1 | 1 | 10/1/2011 | NULL | 12/1/2011
2 | 1 | 10/3/2011 | 11/1/2011 | 12/31/2011
3 | 5 | 10/5/2011 | NULL | NULL
4 | 5 | 10/5/2011 | NULL | NULL
5 | 7 | 11/5/2011 | NULL | 12/1/2011
6 | 10 | 11/2/2011 | NULL | NULL
and I wanted to condense that into a summary table such that:
location | date | hires | rehires | terms
1 | 10/1/2011 | 1 | 0 | 0
1 | 10/3/2011 | 1 | 0 | 0
1 | 11/1/2011 | 0 | 1 | 0
1 | 12/1/2011 | 0 | 0 | 1
1 | 12/31/2011 | 1 | 0 | 0
5 | 10/5/2011 | 2 | 0 | 0
etc.
-- what would that SQL look like? I was thinking it would be something to the effect of:
SELECT
e.location
, -- ?
,SUM(CASE WHEN e.dateHired IS NOT NULL THEN 1 ELSE 0 END) AS Hires
,SUM(CASE WHEN e.dateRehired IS NOT NULL THEN 1 ELSE 0 END) As Rehires
,SUM(CASE WHEN e.dateTerminated IS NOT NULL THEN 1 ELSE 0 END) As Terms
FROM
Employment e
GROUP BY
e.Location
,--?
But I'm not real keen if that's entirely correct or not?
EDIT - This is for SQL 2008 R2.
Also,
INNER JOIN on the date columns assumes that there are values for all three categories, which is false; which is the original problem I was trying to solve. I was thinking something like COALESCE, but that doesn't really make sense either.

Answer 1

I am sure there is probably an easier, more elegant way to solve this. However, this is the simplest, quickest that I can think of this late that works.
CREATE TABLE #Temp
(
Location INT,
Date DATETIME,
HireCount INT,
RehireCount INT,
DateTerminatedCount INT
)
--This will keep us from having to do an insert if does not already exist
INSERT INTO #Temp (Location, Date)
SELECT DISTINCT Location, DateHired FROM Employment
UNION
SELECT DISTINCT Location, DateRehired FROM Employment
UNION
SELECT DISTINCT Location, DateTerminated FROM Employment
UPDATE #Temp
SET HireCount = Hired.HireCount
FROM #Temp
JOIN
(
SELECT Location, DateHired AS Date, SUM(*) AS HireCount
FROM Employment
GROUP BY Location, DateHired
) AS Hired
UPDATE #Temp
SET RehireCount= Rehire.RehireCount
FROM #Temp
JOIN
(
SELECT Location, DateRehired AS Date, SUM(*) AS RehireCount
FROM Employment
GROUP BY Location, DateRehired
) AS Rehire
ON Rehire.Location = #Temp.Location AND Rehire.Date = #Temp.Date
UPDATE #Temp
SET DateTerminatedCount = Terminated.DateTerminatedCount
FROM #Temp
JOIN
(
SELECT Location, DateTerminated AS Date, SUM(*) AS DateTerminatedCount
FROM Employment
GROUP BY Location, DateTerminated
) AS Terminated
ON Terminated.Location = #Temp.Location AND Terminated.Date = #Temp.Date
SELECT * FROM #Temp

Answer 2

How about something like:
with dates as (
select distinct location, d from (
select location, dateHired as [d]
from tbl
where dateHired is not null
union all
select location, dateRehired
from tbl
where dateRehired is not null
union all
select location, dateTerminated
from tbl
where dateTerminated is not null
)
)
select location, [d],
(
select count(*)
from tbl
where location = dates.location
and dateHired = dates.[d]
) as hires,
(
select count(*)
from tbl
where location = dates.location
and dateRehired = dates.[d]
) as rehires,
(
select count(*)
from tbl
where location = dates.location
and dateTerminated = dates.[d]
) as terms
from dates
I don't have a SQL server handy, or I'd test it out.

Answer 3

SELECT * FROM
(SELECT location, dateHired as date, COUNT(1) as hires FROM mytable GROUP BY location, date) H
INNER JOIN
(SELECT location, dateReHired as date, COUNT(1) as rehires FROM mytable GROUP BY location, date) R ON H.location = R.location AND H.dateHired = R.dateRehired
INNER JOIN
(SELECT location, dateTerminated as date, COUNT(1) as terminated FROM mytable GROUP BY location, date) T
ON H.location = T.location AND H.dateHired = T.dateTerminated