To preserve all records from the left stream while including matching right values, which join mode should you select?

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

Answer: (A)

The essential idea is which input’s rows you keep in the result. A left join preserves every row from the left input and attaches matching fields from the right input. If a left row has no corresponding right row, the right-side fields appear as nulls. This exactly matches the goal of keeping all left records while bringing in right values when they exist. The other modes don’t fit: an inner join drops any left rows without a match, a full join includes unmatched rows from both sides, and a right join preserves the right input instead of the left. So, to preserve all records from the left while including matching right values, use the left join.