What is a JOIN in SQL and name at least two types, such as INNER and LEFT OUTER, with brief descriptions.

What is a JOIN in SQL and name at least two types, such as INNER and LEFT OUTER, with brief descriptions.

• A. A JOIN merges a table with itself.
• B. JOIN combines rows from two or more tables; INNER JOIN returns only matching rows; LEFT OUTER JOIN returns all rows from left table plus matching from right.
• C. A JOIN only works with primary keys.
• D. A JOIN duplicates rows.

Answer: (B)

A JOIN in SQL combines rows from two or more tables based on a related column, so you can pull together related data that lives in separate tables. Two common types are inner join, which keeps only the rows where there is a matching value in both tables, and left outer join, which keeps every row from the left table and brings in matching rows from the right table; if there’s no match, the right-side columns show NULL for that row. The order of the tables determines which side is the “left” or the “right,” affecting which rows are preserved when there isn’t a match. This captures the general purpose of joins—linking related data across tables—without being restricted to a self-join (joining a table to itself), and it reflects that a join is not limited to primary keys or to duplicating rows.

A JOIN in SQL combines rows from two or more tables based on a related column, so you can pull together related data that lives in separate tables. Two common types are inner join, which keeps only the rows where there is a matching value in both tables, and left outer join, which keeps every row from the left table and brings in matching rows from the right table; if there’s no match, the right-side columns show NULL for that row. The order of the tables determines which side is the “left” or the “right,” affecting which rows are preserved when there isn’t a match.

This captures the general purpose of joins—linking related data across tables—without being restricted to a self-join (joining a table to itself), and it reflects that a join is not limited to primary keys or to duplicating rows.