求写SQL文的大神帮我解决一下问题

Question

12.表结构如下：
表A： Employee_sn     StartDate        EndDate 
1             '2007-01-02'    '2007-01-03'
1             '2007-01-05'    '2007-01-06'
1             '2007-01-09'    '2007-01-13'
2             '2007-02-02'    '2007-02-03'
3             '2007-04-02'    '2007-04-03'

表B： Employee_sn   CreateDate
1            '2007-01-02'
1            '2007-01-05'   
1            '2007-01-03'
3            '2007-04-02'
1            '2007-01-04'
1            '2007-01-02'
2            '2007-02-02'

要得到的结果：
Employee_sn     StartDate       EndDate       Count
1             '2007-01-02'    '2007-01-03'     3
1             '2007-01-05'    '2007-01-06'     1
1             '2007-01-09'    '2007-01-13'     0
2             '2007-02-02'    '2007-02-03'     1
3             '2007-04-02'    '2007-04-03'     1
这个SQL文怎么写啊，从来都没写过这样的题啊。sql

Answer 1

select *,(select count(*) from b where 
a.Employee_sn=Employee_sn
and  CreateDate between a.StartDate and a.EndDate 
) from a

Answer 2

select a.Employee_sn,a.startDate,a.EndDate,count(a.startDate)+count(b.createDate) as count
from 表A a,表B b
where a.Employee_sn=b.Employee_sn；

Answer 3

select a.Employee_sn,a.startDate,a.EndDate,count(a.startDate)+count(b.createDate) as count
from 表A a,表B b
where a.Employee_sn=b.Employee_sn
group by a.Employee_sn,a.startDate,a.EndDate;