SQL Union
UNION is an operator that concatenates results of different SQL queries:
--do not run this query SELECT columns FROM table1 UNION SELECT columns FROM table2 UNION ... SELECT columns FROM tableN
There is also an operator UNION ALL, and the difference is that UNION returns distinct values, unlike UNION ALL.
Requirements for using UNION operators:
number of columns in
SELECTshould be the samedata types and order of columns should be the same
Compito
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You want to get some info about songs from three decades: 1970s, 1980s, and 1990s. Find the prices of the cheapest and the most expensive songs for each decade in separate queries. You're free to use JOIN, BETWEEN, or any other operators, but you should do three separate queries and concatenate them with UNION.
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Sezione 2. Capitolo 5
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