一行中多列取最大值和最小值

select
     name
    ,greatest(num1,num2,num3,num4) as max_num -- 最大值
    ,least(num1,num2,num3,num4)    as min_num -- 最小值
from (
    select 'a' as name,1 as num1, 3 as num2, 2 as num3,4 as num4
) t1
;