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SQL Problems and solutions S. I. Moiseenko

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Typical mistakes at the solution of SELECT statement exercises

Database «Ships»

Exercise #46 page 3

In conclusion, I adduce one more solution with such mistake, but without using outer joins.

Solution 3.1.3

Console

Execute

SELECT a.ship, b.displacement, b.numguns
FROM Outcomes a, Ships c, Classes b
WHERE a.battle='Guadalcanal' AND
 a.ship = c.name AND
 c.class = b.class
UNION
SELECT a.ship, NULL AS displacement, NULL AS numguns
FROM Outcomes a
WHERE a.battle = 'Guadalcanal' AND
 a.ship NOT IN (SELECT name 
 FROM Ships
 );

Let`s note that the first offered solution would return right result for such lead ship. That`s why that to solve this task we need to append the first solution to the second. The ways how should not to "append" solution, you can see in the Chapter four.

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aggregate functions ALL ASCII AVG Battles Bezhaev Bismarck C.J.Date Cartesian product CASE cast CHAR CHARINDEX classes COALESCE common table expressions comparison predicates Computer firm CONVERT correlated subqueries COUNT CTE data type conversion database schema DATEDIFF DATEPART DATETIME DELETE DISTINCT duplicates EXCEPT exercise (-2) exercise 19 exercise 23 exercise 32 exercise 37 exercise 39 exercise 46 exercise 54 exercise 55 exercise 56 exercise 57 exercise 7 exercise 70 exercise 8 exercises EXISTS FROM FULL JOIN GROUP BY More tags

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SQL Problems and solutions

S. I. Moiseenko

Typical mistakes at the solution of SELECT statement exercises

Database «Ships»

Exercise #46 page 3