Question 7: Can you tell me what the difference of two SQL statements at performance of execution?
Statement 1:

 程序代码
if NOT EXISTS ( select * from publishers where state = 'NY')
begin
Select 'Sales force needs to penetrate New York market'
end
else
begin
Select 'We have publishers in New York'
end
Statement 2:
if EXISTS ( select * from publishers where state = 'NY')
begin
Select 'We have publishers in New York'
end
else
begin
Select 'Sales force needs to penetrate New York market'
end

Answer 7：不同点:执行时的事务数,处理时间,从客户端到服务器端传送的数据量大小

Question8: How can I list all California authors regardless of whether they have written a book?
In database pubs, have a table authors and titleauthor , table authors has a column state, and titleauhtor have books each author written.
CA behalf of california in table authors.
Answer 8：
select * from  authors where state='CA'

Question9: How can I get a list of the stores that have bought both 'bussiness' and 'mod_cook' type books?
In database pubs, use three table stores,sales and titles to implement this requestment.
Now I want to get the result as below:
stor_id stor_name                               
------- ----------------------------------------
…
7896    Fricative Bookshop
…
…
…
Answer 9：

 程序代码
select distinct a.stor_id, a.stor_name from stores a,sales b,titles c
where a.stor_id=b.stor_id and b.title_id=c.title_id and c.type='business' and
exists(select 1 from sales k,titles g where stor_id=b.stor_id
and k.title_id=g.title_id and g.type='mod_cook')