I use following statement to select the records I want :

SELE a.po,a.item,a.qty,b.price,a.qty*b.price AS amt ;
FROM purchase a,stock b ;
WHERE a.item = b.item

However, when stock table has a item that supplied by 2 supplier, then my output will go wrong, for eg :

purchase table
po item qty
123 a 10

stock table
item supplier price
a abc 10
a bcd 9


then I get the result

123,a,10,10,100
123,a,10,9,90

How can I solve this problem by single SQL SELECT statement.

Thank In advance.