MS-SQL - union all 예제

select * from grpSignMain join (
select 'vac' as category, vacMainIdx as idx, vacStartDate as startDate, vacEndDate as endDate,Null as overType from grpSignVacation
union all
select 'dil' as category, dilMainIdx as idx, dilStartDate as startDate, dilEndDate as endDate,Null as overType from grpSignDiligence
union all
select 'over' as category, overMainIdx as idx, overStartDate as startDate, overEndDate as endDate,overType from grpSignOverTime
) as tab on mainIdx = idx order by idx

Null as overType : 특정 컬럼을 가상으로 만들때 사용