当单个员工 ID 具有多个日期值且仅需要最新日期时，如何使用 max function 返回单个记录

Question

We have Employees that will have several BEG_DATE returns and we only need the record that has the latest date. I can use the MAX to return that date when I apply the second query - but how can I use it on this query below?

SELECT REPLACE(EMPLOYEE.EMPLOYEE , ',', '') AS EMPLOYEE_ID, A_VALUE, DB.EMPLOYEE.EMP_STATUS, DB.HRHISTORY.BEG_DATE
    FROM DB.PERSHST
    INNER JOIN WDWASIS ON WDWASIS.FILENAME = 'LEAVE_TYPE_NAME' 
           AND PERSHST.REASON_01 = WDWASIS.ALPHA_DEF2
           AND PERSHST.REASON_02 = WDWASIS.ALPHA_DEF3
    INNER JOIN DB.EMPLOYEE ON DB.PERSHST.EMPLOYEE = DB.EMPLOYEE.EMPLOYEE
    INNER JOIN DB.HRHISTORY ON DB.HRHISTORY.EMPLOYEE = DB.EMPLOYEE.EMPLOYEE AND DB.HRHISTORY.COMPANY = DB.EMPLOYEE.COMPANY AND DB.HRHISTORY.FLD_NBR = 20 
    WHERE DB.EMPLOYEE.EMP_STATUS LIKE 'L%' AND DB.HRHISTORY.A_VALUE LIKE 'L%' 

This query works of course when I have a single employee - but how can I feed this into the query above?

SELECT DB.HRHISTORY.EMPLOYEE, MAX(DB.HRHISTORY.BEG_DATE)
FROM DB.HRHISTORY
WHERE DB.HRHISTORY.EMPLOYEE ='0'
GROUP BY DB.HRHISTORY.EMPLOYEE

Answer 1

Create a table with the max(date) per employee and join to it on employeeId and date. Or, something like this...

    with emp_max_date as
        (
        SELECT DB.HRHISTORY.EMPLOYEE as employee_id, MAX(DB.HRHISTORY.BEG_DATE) as recent_date
        FROM DB.HRHISTORY
        GROUP BY DB.HRHISTORY.EMPLOYEE
        )
    SELECT REPLACE(EMPLOYEE.EMPLOYEE , ',', '') AS EMPLOYEE_ID, A_VALUE, DB.EMPLOYEE.EMP_STATUS, DB.HRHISTORY.BEG_DATE
        FROM DB.PERSHST
        INNER JOIN WDWASIS ON WDWASIS.FILENAME = 'LEAVE_TYPE_NAME' 
               AND PERSHST.REASON_01 = WDWASIS.ALPHA_DEF2
               AND PERSHST.REASON_02 = WDWASIS.ALPHA_DEF3
        INNER JOIN DB.EMPLOYEE ON DB.PERSHST.EMPLOYEE = DB.EMPLOYEE.EMPLOYEE
        INNER JOIN DB.HRHISTORY ON DB.HRHISTORY.EMPLOYEE = DB.EMPLOYEE.EMPLOYEE AND DB.HRHISTORY.COMPANY = DB.EMPLOYEE.COMPANY AND DB.HRHISTORY.FLD_NBR = 20 
        join emp_max_date eb on eb.employee_id = db.employee.employee and eb.recent_date = db.hrhistory.beg_date
        WHERE DB.EMPLOYEE.EMP_STATUS LIKE 'L%' AND DB.HRHISTORY.A_VALUE LIKE 'L%'