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# Typical errors at solution of exercises (database "Computer firm")

AuthorS. Moiseenko

## Exercise 2

Find printer makers. Result set: maker.

AuthorS. Moiseenko

## Exercise 7

Find out the models and prices for all the products (of any type) produced by maker B.

AuthorS. Moiseenko

## Exercise 8

Find out the makers that sale PCs but not laptops.

AuthorS. Moiseenko

## Exercise 14

For Product table, receive result set in the form of a table with columns: maker, pc, laptop, and printer. For each maker, this table must include "yes" if a maker has products of corresponding type or "no" otherwise. In the first case (yes), specify in brackets (without spaces) the quantity of available distinct models of corresponding type (i.e. being in PC, Laptop, and Printer tables).

AuthorS. Moiseenko

## Exercise 16

Find the pairs of PC models having similar speeds and RAM. As a result, each resulting pair is shown only once, i.e. (i, j) but not (j, i). Result set: model with high number, model with low number, speed, and RAM.

AuthorS. Moiseenko

## Exercise 18

Find the makers of the cheapest color printers. Result set: maker, price .

AuthorS. Moiseenko

## Exercise 23

Find the producers, which produce both PC with speed not less than 750MHz, and Laptops with speed not less than 750 MHz. Output: Maker.

AuthorS. Moiseenko

## Exercise 24

Find the number of product's model (PC, PC-laptop or printer) that has the highest price. Output: model.

AuthorS. Moiseenko

## Exercise 25

Find the printer makers which also produce PCs with the lowest RAM and the highest-speed processor among PCs with the lowest RAM. Result set: maker.

AuthorS. Moiseenko

## Exercise 26

Define the average price of the PCs and laptops produced by maker A. Result set: single total price.

AuthorS. Moiseenko

## Exercises 27 & 28

Define the average size of the PC hard drive for each maker that also produces printers. Result set: maker, average capacity of HD.
Define the average HD size (single value for all makers) of PCs produced by those makers that also produce printers. Result set: average size of HD.


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