Which SQL JOIN returns all rows from the left table and matching rows from the right, with NULLs for non-matches?

Which SQL JOIN returns all rows from the left table and matching rows from the right, with NULLs for non-matches?

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

Answer: (B)

Left joins preserve every row from the left table and attach matching data from the right, filling the right-side fields with NULLs when there’s no match. This means you keep all the left-side records even if there isn’t related data on the right. For example, if you have a list of customers and a list of their orders, a left join on customers.id = orders.customer_id will show every customer. If a customer hasn’t placed an order, the order columns will be NULL, while customers with orders will show the corresponding order data. The other types don’t fit this requirement: an inner join would drop customers with no orders, a right join would prioritize the right table, and a full join would bring in all rows from both sides, with NULLs where there are no matches.

Left joins preserve every row from the left table and attach matching data from the right, filling the right-side fields with NULLs when there’s no match. This means you keep all the left-side records even if there isn’t related data on the right.

For example, if you have a list of customers and a list of their orders, a left join on customers.id = orders.customer_id will show every customer. If a customer hasn’t placed an order, the order columns will be NULL, while customers with orders will show the corresponding order data.

The other types don’t fit this requirement: an inner join would drop customers with no orders, a right join would prioritize the right table, and a full join would bring in all rows from both sides, with NULLs where there are no matches.