关于SQL中的Except

 1 use test1
 2 select address_district,COUNT(address_district) as total from hr_personal_test group by address_district with rollup;
 3 create table test1 (id int);
 4 create table test2 (num int);
 5 
 6 --1 1(1,2,3) 2(1,4)
 7 --insert into test1 select 1 union select 2 union select 3
 8 --insert into test2 select 1 union select 4
 9 
10 --select id from test1 except select num from test2;-------返回结果2，3
11 
12 
13 delete from test1 ;
14 delete from test2;
15 --2 1(1,2) 2(1,2,3,4)
16 --insert into test1 select 1 union select 2 
17 --insert into test2 select 1 union select 2 union select 3 union select 4
18 --select id from test1 except select num from test2; --------返回结果 没有
19 
20 delete from test1 ;
21 delete from test2;
22 --3 1(1,2) 2(3,4) 
23 insert into test1 select 1 union select 2 
24 insert into test2 select 3 union select 4
25 select id from test1 except select num from test2-------- 返回结果 1,2
26 
27 delete from test1 ;
28 delete from test2;
29 --4 1(1,2,3) 2(1,2)
30 insert into test1 select 1 union select 2 union select 3
31 insert into test2 select 1 union select 2 
32 select id from test1 except select num from test2--------返回结果3

create table test1(id int ,name nvarchar(20))
create table test2(id int ,post nvarchar(4))

insert into test1 (name) values (‘a‘),(‘b‘),(‘b‘),(‘c‘)
insert into test2 (post) values(‘a‘)

select name from test1 except select post from test2--------返回 b,c

select name from test1 where name not in(select post from test2)---------返回 b,b,c