SQL查询：1个员工职位/岗位为2个结果

Question

我有一份当前职位/职位的员工名单，其职位和工作开始日期的开始日期。

我需要一个查询来生成当前位置作为一个结果，如果该位置的开始日期与就业开始日期不匹配，则显示作为第二结果的历史位置。

数据

[Employee Number]   Position    [Start Date]    [Employment Start Date]
-----------------------------------------------------------------------
12345               Admin       01/01/2017      01/01/2016

产量

[Employee Number]   Position    [Start Date]    [End Date]
-----------------------------------------------------------
12345               Admin       01/01/2017      NULL
12345               Historic    01/01/2016      31/12/2017

Answer 1

SELECT 
       [Employee Number],
       [Position],
       [Start Date],
       NULL AS [End Date]
FROM 
      TABLE_NAME

UNION ALL

SELECT 
       [Employee Number],
       'Historic' AS [Position],
       [Employment Start Date] AS [Start Date],
       DATEADD( DAY,-1,[Start Date] ) AS [End Date]
FROM 
      TABLE_NAME
WHERE 
      [Start Date] <> [Employment Start Date]

Answer 2

你可以使用union all：

select employee_number, position, start_date, cast(null as date) end_date
from data
union all
select employee_number, position, employment_start_date, dateadd(day, -1, start_date)
from data
where employment_start_date < start_date;

Answer 3

            WITH table1 AS (
                SELECT * FROM (
                    VALUES
                        ('12345', 'Admin','2017-01-01','2016-01-01')

                    ) AS a (EmployeeNumber, position,StartDate,EmploymentStartDate)
            )

            select EmployeeNumber, position,StartDate, CASE WHEN StartDate!=EmploymentStartDate THEN NULL ELSE EmploymentStartDate END AS EndDate  from table1
            union
            Select EmployeeNumber,'Historic',EmploymentStartDate as StartDate,DATEADD(dd,-1,DATEADD(yy,1,StartDate)) AS EndDate
            From table1 where StartDate!=EmploymentStartDate