Агрегирование нескольких столбцов в SQL

Question

Предположим, у меня есть таблица, которая выглядит следующим образом

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

, и я хотел сжать это в сводную таблицу так:

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

и т.д.

- как бы выглядел этот SQL? Я думал, что это будет что-то с эффектом:

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
  ,--?

Но я не очень заинтересован, если это совершенно правильно или нет?

РЕДАКТИРОВАТЬ - Это для SQL 2008 R2.

Кроме того,

INNER JOIN в столбцах даты предполагает наличие значений для всех трех категорий, что неверно; это первоначальная проблема, которую я пытался решить. Я думал что-то вроде COALESCE, но это тоже не имеет смысла.

Answer 1

Как насчет чего-то вроде:

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

У меня нет удобного сервера SQL, или я бы его протестировал.

Answer 2

Я уверен, что, возможно, есть более простой и элегантный способ решить эту проблему. Тем не менее, это самое простое, самое быстрое, что я могу думать об этом конце, которое работает.

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 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