select
min([Date]) as [Date]
from
(select min(Check_Date) as [Date] from T1
union all
select min(Bill_Date ) from T2
union all
select min(RBill_Date) from T3) a
min([Date]) as [Date]
from
(select min(Check_Date) as [Date] from T1
union all
select min(Bill_Date ) from T2
union all
select min(RBill_Date) from T3) a
(select check_date aa from t1
union all
select bill_date from t2
union all
select rbill_date from t3)a
select min(dt)
from (
select Check_Date as 'dt' from T1
union
select Bill_Date from T2
union
select RBill_Date from T3
)t如果是关联字段比较:select case when T1.Check_Date<T2.Bill_Date
and T1.Check_Date<T3.RBill_Date
then T1.Check_Date
when T1.Check_Date>T2.Bill_Date
and T2.Bill_Date<T3.RBill_Date
then T2.Bill_Date
else T3.RBill_Date
end
from T1
join T2 on T1.关联字段=T2.关联字段
join T3 on T1.关联字段=T3.关联字段
minDate = case
when T1.Check_Date < T2.Bill_Date and T1.Check_Date < T3.RBill_Date
then T1.Check_Date
when T2.Bill_Date < T3.RBill_Date
then T2.Bill_Date
else T3.RBill_Date
end
from
T1,T2,T3
where
T1.关联字段 = T2.关联字段
and
T2.关联字段 = T3.关联字段