What does a FULL OUTER JOIN do in SQL?

What does a FULL OUTER JOIN do in SQL?

• A. Returns Only Rows That Have Matches in Both Tables
• B. Returns All Rows From The Left Table With Matches From The Right, Or NULL If No Match
• C. Returns All Rows From The Right Table With Matches From The Left, Or NULL If No Match
• D. Returns All Rows From Both Tables, With NULLs Where There Is No Match

Answer: (D)

A FULL OUTER JOIN returns all rows from both tables, with NULLs filled in wherever there isn’t a matching row on the other side. It combines the effect of taking every row from both tables and pairing up those that meet the join condition, while also preserving rows that have no counterpart in the other table. This means you’ll see every row from the first table joined to matching rows in the second, and also every row from the second table joined to matching rows in the first. If a row in one table has no match, the columns from the other table appear as NULL. For example, if you have customers and orders, you’ll get every customer and every order, with NULLs where a customer has no orders or an order references a non-existent customer. In contrast, an inner join would only show rows where there’s a match in both tables, a left join would include all rows from the left table with NULLs for missing right-side data, and a right join would do the opposite. Full outer join is the combination that covers all rows from both sides.

A FULL OUTER JOIN returns all rows from both tables, with NULLs filled in wherever there isn’t a matching row on the other side. It combines the effect of taking every row from both tables and pairing up those that meet the join condition, while also preserving rows that have no counterpart in the other table.

This means you’ll see every row from the first table joined to matching rows in the second, and also every row from the second table joined to matching rows in the first. If a row in one table has no match, the columns from the other table appear as NULL. For example, if you have customers and orders, you’ll get every customer and every order, with NULLs where a customer has no orders or an order references a non-existent customer.

In contrast, an inner join would only show rows where there’s a match in both tables, a left join would include all rows from the left table with NULLs for missing right-side data, and a right join would do the opposite. Full outer join is the combination that covers all rows from both sides.