出道distinct相关的sql题给大家做做

这几天在做sql编译相关的东西, 自己弄了个题目,连资深数据库开发人员都可能会搞错. 以下sql中哪些执行时会报错? (适于所有常见DBMS)
1.

select
   distinct col
from
  tbl

2.

select
  distinct col1,
  distinct col2
from
  tbl  

3.

select
   count(distinct col% 10)
from
  tbl

 4.

select
   length(distinct col1% 10)
from
  tbl

 5.

select
   sum(distinct col1% 10),  
   sum(distinct col1% 9)
from
  tbl

 6.

select
  distinct col1,
  count(distinct col2)
from
  tbl

 

 7.

select
  sum(distinct col1 % 10),
  count(distinct col2 % 9)
from
  tbl

 8.

select
  max(distinct substr(col1, 1, 10)),
  count(distinct col2 % 9)
from
  tbl