Which join would you use to ensure you keep all rows from the left query and include matches from the right query?

Which join would you use to ensure you keep all rows from the left query and include matches from the right query?

• A. Right outer
• B. Full outer
• C. Inner
• D. Left outer

Answer: (D)

This question is about preserving every row from the left input while bringing in matching data from the right. A left outer join does exactly that: it returns all rows from the left table and the matching rows from the right table; if there’s no match on the right, the right-side columns appear as NULL. For example, joining customers (left) with orders (right) on customer_id will include every customer, and for those with no orders, the order fields will be NULL. Other joins don’t fit: an inner join would drop left rows with no matches, a right outer join would keep all right rows, and a full outer join would keep all rows from both sides regardless of matches.

This question is about preserving every row from the left input while bringing in matching data from the right. A left outer join does exactly that: it returns all rows from the left table and the matching rows from the right table; if there’s no match on the right, the right-side columns appear as NULL. For example, joining customers (left) with orders (right) on customer_id will include every customer, and for those with no orders, the order fields will be NULL. Other joins don’t fit: an inner join would drop left rows with no matches, a right outer join would keep all right rows, and a full outer join would keep all rows from both sides regardless of matches.