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MYSQL Consider the sql statement "select * from t1 UNION t2" where t1 and t2 are...

MYSQL

Consider the sql statement "select * from t1 UNION t2" where t1 and t2 are two sets (tables).
This query executes without any errors.
Assume t1 has n columns. How many columns does t2 have? How many columns
will the resultset have?

Is it possible for the result set to have more records than the combination of t1 and t2
(for example say t1 has 8 records and t2 has 8 records)
is it possible for the resultset to have 18 rows?
it it possible for the resultset to have 10 rows?
If yes, under what scenario is it possible to have 10 rows?
is it possible for the resultset to have 16 rows?
If yes under what scenario is it possible to have 16 rows?

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Answer #1

--> T2 should also have n columns because for UNION to work properly both tables should have same number of columns.

--> No, it is not possible because UNION will combine rows in both of them.

--> It is not possible for resultset to have 18 rows because combinely they have only 16 rows.

--> Yes it is possible for resultset to have 10 rows, when 6 rows are common in both of them.

--> Yes it is possible for resultset to have 16 rows, when 2 rows are common in both of them.

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