SQL取行最大值

create table T(A decimal(10,1), B decimal(10,1), C decimal(10,1), D decimal(10,1), E decimal(10,1))
insert T select -21.5,-15.0,-5.0, null, null
union all select -5.5,-11.5,null, null, null
union all select -1.0,-16.5,-10.5, null, null

SELECT * FROM T
select *,
max_value=(
select max(A) from( select A union all select B union all select C union all select D union all select E)tmp
)
from T