sql 查询一行内几列的平均值，最大值，最小值，怎么写

oracle的话直接用greatest函数，sql server的话照这么写： select t1.name, max(t1.a) maxnum,min(t1.a) minnum,avg(t1.a) avgnum from (select name,num1 a from tb1 union all select name,num2 a from tb1 union all select name,num3 a from tb1 union all select name,num