sql内部联接不适用于内部联接

Question

I have tables like customer, items, manufacture, order, stock.. refer http://www.oninit.com/manual/informix/english/docs/gn7382/4366.pdf

I want to get the first and last names of every person (and the city and state they live in) who has ordered something made by the company Smith . Include the description (from the stock table).

If I execute the first part as

select c.fname, c.lname, c.city, c.state from customer c join orders o using (customer_num)
join items i using(order_num)
join manufact m using(manu_code)  where m.manu_name = 'Smith' ;

I get 8 records which is correct, I further want the description from stock table for these records, so I created a join on stock table like

select c.fname, c.lname, c.city, c.state, s.description from customer c join orders o using (customer_num)
join items i using(order_num)
left join (manufact m join stock s on m.manu_code=s.manu_code) on m.manu_code = i.manu_code where m.manu_name = 'Smith';

Now, its giving me 24 records which I dont expect. How do I write a nested query to get only 8 records?

Stock schema enter image description here

Answer 1

You have 24 stock items from the manufacturer. You need to decide what you want to display.

Your query is doing what you want it to do.

I would say, though, that structuring the query without the nested join is simpler. You also left out the description :

select c.fname, c.lname, c.city, c.state, s.description
from customer c join
     orders o
     using (customer_num) join
     items i
     using (order_num) join
     manufact m
     using (manu_code) join
     stock s
     using (manu_code)
where m.manu_name = 'Smith';

I also suspect that stock has some sort of itemid that you should also be joining on.

Answer 2

You can see from your stock table that, there are multiple stock_num for a manu_code . There are 3 stock_num for the corresponding manu_code for m.manu_name = 'Smith'

Thats why your query returns 8*3 = 24 rows.

To get the appropriate result, you can

select c.fname, c.lname, c.city, c.state, s.description
from customer c 
     join orders o using (customer_num) 
     join items i using (order_num) 
     join manufact m using (manu_code) 
     join (select description from stock group by manu_code) AS s ON s.manu_code = m.manu_code
where m.manu_name = 'Smith'