If two datasets participate in a one-to-one join with exact key correspondence and no missing values, the number of output features equals the number of features in each input.

If two datasets participate in a one-to-one join with exact key correspondence and no missing values, the number of output features equals the number of features in each input.

• A. True
• B. Not determinable
• C. Depends
• D. False

Answer: (A)

When two datasets join on a key with a one-to-one match and every key exists in both inputs, each input row has exactly one counterpart in the other input. The join produces one output row for each key, so the number of output features (rows) stays the same as the number of features in either input. What changes is the content: you combine attributes from both inputs into each joined row (typically with suffixes if there are overlapping attribute names). So the row count matches across inputs, even though the attribute set in the output is effectively the union of both inputs' attributes. If the join were many-to-one, one-to-many, or had missing matches, the row count would differ.

When two datasets join on a key with a one-to-one match and every key exists in both inputs, each input row has exactly one counterpart in the other input. The join produces one output row for each key, so the number of output features (rows) stays the same as the number of features in either input. What changes is the content: you combine attributes from both inputs into each joined row (typically with suffixes if there are overlapping attribute names). So the row count matches across inputs, even though the attribute set in the output is effectively the union of both inputs' attributes. If the join were many-to-one, one-to-many, or had missing matches, the row count would differ.