The left join part was fine, I had that logic pretty quick.
First, clarify the function's current behavior and the exact semantics of the boolean flag (e.g., true means skip unmatched rows). Then, outline a clean implementation that separates the join logic from the filtering step, ensuring backward compatibility by defaulting to the existing left join behavior. Finally, discuss edge cases and trade-offs such as performance and memory usage.
Pro tip: Mention that you would add the flag as an optional parameter with a default value that preserves the current left join behavior, and consider using an enum instead of a boolean for future extensibility (e.g., to support inner, right, or full joins).
Ask questions to confirm the function's current join behavior, the meaning of the boolean flag, and whether the flag should default to preserving existing behavior. Ensure you understand what 'empty values' means for missing columns (e.g., null, empty string).
Decide how to add the flag: as an optional parameter with a default value that maintains backward compatibility. Consider naming and type (boolean vs. enum) for clarity and future extension.
Describe how you would modify the join logic: perform the left join as before, then if the flag indicates skipping unmatched rows, filter out rows where the key from the right dataset is missing. Alternatively, conditionally include unmatched rows during the join.
Discuss how to handle missing values (null vs. empty string), duplicate keys, and type mismatches. Ensure the flag works consistently regardless of data types.
Mention performance implications (e.g., filtering after join vs. during join) and memory usage. Suggest unit tests for both flag states and edge cases.
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