SQL General Concepts 3

Question 1

Which type of JOIN returns only rows with matching values in both tables?

Accepted Answer

INNER JOIN

Answer

An INNER JOIN returns only rows where the join condition matches in both tables.

Question 2

What does a foreign key establish?

Accepted Answer

A link between two tables

Answer

A foreign key references a primary key in another table, enforcing referential integrity.

Question 3

Which aggregate function counts the number of rows?

Accepted Answer

COUNT()

Answer

COUNT() returns the number of rows matching the query.

Question 4

What does the GROUP BY clause do?

Accepted Answer

Groups rows sharing a value for aggregation

Answer

GROUP BY groups rows with the same values so aggregate functions can summarize them.

Question 5

Which clause filters results after aggregation?

Accepted Answer

HAVING

Answer

HAVING filters groups after aggregation, unlike WHERE which filters rows before.

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