Exercise #18 (tips and solutions)

In the following solution

SELECT c.maker, a.priceA price
FROM (SELECT MIN(price) priceA
FROM Printer
WHERE Color ='y'
) a INNER JOIN
Printer b ON a.priceA = b.price INNER JOIN
Product c ON b.model = c.model;

Surely, joining on price might be replaced by simple comparison:

WHERE price = (SELECT min(price) priceA
FROM Printer
WHERE Color ='y'
)

A mistake in the query is not related to said above, but to the fact that the solution determines ANY printers which have price coincident with a minimal price for color printers. Database includes corresponding items. As a result, we obtain

Meanwhile, correct answer gives only one row:

Second row is not related to color printer. You can be easyly convinced of it if you’ll include additional columns in SELECT clause:

SELECT c.maker, a.priceA price, color, b.type

which give

Second mistake is in possible duplicates, as a maker may have several printers having the same price.

To return to discussion of exercise #18

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