ITPEC IP October 2018 Question 27
The “Sales Details” table and the “Products” table are managed in a relational database. What is the total number of notebooks sold?
Sales Details
Products
Explanation
120 — look up the product code of Notebook in Products, then add Number_sold over every Sales Details row with that code.
- •Products: Notebook has Product_code S003
- •Sales Details rows with S003: voucher H001 sold 40, voucher H002 sold 80
- •Total: 40 + 80 = 120
This is a join of the two tables on Product_code, keeping the rows whose Product_name is Notebook, then SUM(.
Answer (c)
Why not others:
- •(a) 40 — only voucher H001's notebook row; H002 also sold notebooks
- •(b) 80 — only voucher H002's notebook row
- •(d) 200 — adds every row, 20 + 40 + 60 + 80, pencils and erasers included
Key rule: A code in one table means nothing until it is looked up in the table it refers to; filter on it, then aggregate every matching row, not just the first.
Databases · AI-written, may contain errors
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