Which statement best describes a left join?

Which statement best describes a left join?

• A. It returns all rows from the left table regardless of matches
• B. It returns all rows from the right table regardless of matches
• C. It returns all rows from the left table, and matching rows from the right; if no match, the right side is null
• D. It returns all rows from both tables regardless of matches

Answer: (C)

A left join keeps every row from the left table and brings in matching rows from the right table. If there’s no corresponding row in the right table, the right-side columns show NULL. This behavior—preserving all left rows while filling in matches from the right, and using NULLs when there’s no match—defines a left join. So the statement that best describes it is: it returns all rows from the left table, and matching rows from the right; if no match, the right side is null. The other descriptions refer to different join behaviors: returning all rows from the right table is a right join; returning all rows from both tables regardless of matches is a full outer join; mentioning only the left table without describing how the right side is handled misses the key aspect of bringing in right-side data for matches.

A left join keeps every row from the left table and brings in matching rows from the right table. If there’s no corresponding row in the right table, the right-side columns show NULL. This behavior—preserving all left rows while filling in matches from the right, and using NULLs when there’s no match—defines a left join.

So the statement that best describes it is: it returns all rows from the left table, and matching rows from the right; if no match, the right side is null.

The other descriptions refer to different join behaviors: returning all rows from the right table is a right join; returning all rows from both tables regardless of matches is a full outer join; mentioning only the left table without describing how the right side is handled misses the key aspect of bringing in right-side data for matches.