Sum only for Employee ID's present in latest snapshot - sql

Question

I have a database with a row per month for each employee working in our company. So, if employee A has been working for our company from July 2016 till now, this person has approx. 24 rows (one row for each month she was in service).
I'm trying to summarize the experience each of the current employees have in a particular function. So, if employee A has worked 6 months in Sales and 18 months in Marketing, then I count the number of rows this employee has Sales or Marketing in the column indicating the function.
I have created a code which does seems to count the functional experience per employee, but it double counts data. It does not take the latest snapshot as starting point.
SELECT A.EMPLOYEE_ID,
SUM(CASE WHEN A.FUNCTION_CODE ='CUS' THEN 1 ELSE 0 END) AS EXP_CUS,
SUM(CASE WHEN A.FUNCTION_CODE ='MKT' THEN 1 ELSE 0 END) AS EXP_MKT
FROM [dbname].[AGL_V_HRA_FE_R].[VW_HRA_EMPLOYEE_DETAIL] AS A INNER JOIN [dbname].[AGL_V_HRA_FE_R].[VW_HRA_EMPLOYEE_DETAIL] AS B ON A.EMPLOYEE_ID = B.EMPLOYEE_ID
WHERE B.WORKLEVEL_CODE > '1'
GROUP BY A.EMPLOYEE_ID
I expected the output for employee A to be EXP_CUS = 6 and EXP_MKT = 18. Instead, the output for both is much higher as it is double counting rows. When I add the line AND B.SNAPSHOT_DATE = '2019-06-30', the output is correct. I don't like to manually adjust the code every month and rather refer to the latest snapshot date.
ADDED
The original table looks like this
SNAPSHOT_DATE | EMPLOYEE_ID | FUNCTION_CODE
2019-06-30 | 000000001 | CUS
2019-06-30 | 000000002 | MKT
2019-05-31 | 000000001 | CUS
2019-05-31 | 000000002 | MKT
2019-04-30 | 000000001 | MKT
2019-04-30 | 000000002 | MKT
The desired output would be
EMPLOYEE_ID | EXP_CUS | EXP_MKT
000000001 | 2 | 1
000000002 | 0 | 3

Answer 1

You can use PIVOT to get your desired result as below-
SELECT EMPLOYEE_ID,
ISNULL([CUS],0) AS [EXP_CUS],
ISNULL([MKT],0) AS [EXP_MKT]
FROM
(
SELECT EMPLOYEE_ID,FUNCTION_CODE,COUNT(SNAPSHOT_DATE) T
FROM your_table
GROUP BY EMPLOYEE_ID,FUNCTION_CODE
)P
PIVOT(
SUM(T)
FOR FUNCTION_CODE IN ([CUS],[MKT])
)PVT
Output is-
EMPLOYEE_ID EXP_CUS EXP_MKT
000000001 2 1
000000002 0 3

Answer 2

I don't understand why you are using a self join. This seems to do what you want:
SELECT ED.EMPLOYEE_ID,
SUM(CASE WHEN ED.FUNCTION_CODE ='CUS' THEN 1 ELSE 0 END) AS EXP_CUS,
SUM(CASE WHEN ED.FUNCTION_CODE ='MKT' THEN 1 ELSE 0 END) AS EXP_MKT
FROM [dbname].[AGL_V_HRA_FE_R].[VW_HRA_EMPLOYEE_DETAIL] ed
WHERE ED.WORKLEVEL_CODE > '1'
GROUP BY ED.EMPLOYEE_ID;
If you only want employees with the most recent snapshot date, then you can use window functions:
SELECT ED.EMPLOYEE_ID,
SUM(CASE WHEN ED.FUNCTION_CODE ='CUS' THEN 1 ELSE 0 END) AS EXP_CUS,
SUM(CASE WHEN ED.FUNCTION_CODE ='MKT' THEN 1 ELSE 0 END) AS EXP_MKT
(SELECT ED.*,
MAX(SNAPSHOT_DATE) OVER () as OVERALL_MAX_SNAPSHOT_DATE,
MAX(SNAPSHOT_DATE) OVER (PARTITION BY EMPLOYEE_ID) as EMPLOYEE_MAX_SNAPSHOT_DATE
FROM [dbname].[AGL_V_HRA_FE_R].[VW_HRA_EMPLOYEE_DETAIL] ED
) ED
WHERE ED.WORKLEVEL_CODE > '1' AND
EMPLOYEE_MAX_SNAPSHOT_DATE = OVERALL_MAX_SNAPSHOT_DATE
GROUP BY ED.EMPLOYEE_ID;