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