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SQL Problems and solutions S. I. Moiseenko

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SQL console

back go forward

SELECT statement

Conventional set-theoretic operations and the SELECT statement

Union page 2

Let's consider the task.

Find out all available products of the producer 'B'. Output: model, type.

One laptop and three PCs are in the database from maker 'B', and all the PCs are of the same model.

If we'll use UNION ALL, we get all these items. Using UNION, the duplicates will be excluded from the result:

Console

Execute

SELECT p.model, p.type FROM pc JOIN Product p ON PC.model=p.model WHERE maker='B'
UNION ALL
SELECT p.model, p.type FROM printer pr JOIN Product p ON pr.model=p.model WHERE maker='B'
UNION ALL
SELECT p.model, p.type FROM laptop lp JOIN Product p ON lp.model=p.model WHERE maker='B';

model	type
1121	PC
1121	PC
1121	PC
1750	Laptop

Console

Execute

SELECT p.model, p.type FROM pc JOIN Product p ON PC.model=p.model WHERE maker='B'
UNION 
SELECT p.model, p.type FROM printer pr JOIN Product p ON pr.model=p.model WHERE maker='B'
UNION
SELECT p.model, p.type FROM laptop lp JOIN Product p ON lp.model=p.model WHERE maker='B';