What is a natural join?

What is a natural join?

• A. A natural join is a special case of an inner join that compares all columns with the same name in both tables.
• B. It returns all rows from both tables regardless of common columns.
• C. It uses the ON clause to specify join conditions.
• D. It is an outer join that preserves unmatched rows.

Answer: (A)

Natural join hinges on matching columns that share the same name in both tables. It behaves like an inner join, but the join condition is implicit: it automatically joins rows where those common-named columns are equal, and it returns each shared column only once in the result. This means you get only rows where the values match on all common columns, with duplicates for the non-common columns brought together. The other ideas don’t fit because - returning all rows from both tables regardless of common columns describes a cartesian product or an outer-join-like behavior, not a natural join. - using an ON clause specifies explicit join conditions chosen by you, whereas a natural join determines its conditions automatically from the shared column names. - an outer join that preserves unmatched rows would keep non-matching rows from one or both tables, which a natural join does not do.

Natural join hinges on matching columns that share the same name in both tables. It behaves like an inner join, but the join condition is implicit: it automatically joins rows where those common-named columns are equal, and it returns each shared column only once in the result. This means you get only rows where the values match on all common columns, with duplicates for the non-common columns brought together.

The other ideas don’t fit because

• returning all rows from both tables regardless of common columns describes a cartesian product or an outer-join-like behavior, not a natural join.

• using an ON clause specifies explicit join conditions chosen by you, whereas a natural join determines its conditions automatically from the shared column names.

• an outer join that preserves unmatched rows would keep non-matching rows from one or both tables, which a natural join does not do.