フリー問題

問題文

A report adds a bonus column to a salary column and some rows come back empty in the total. Which statement about how nulls behave in expressions is correct?

選択肢

1. An arithmetic expression that contains a null evaluates to null while the comparison operators are the exception that treat it as equal to zero.
2. An arithmetic expression that contains a null evaluates to null while the concatenation operator is the exception that treats it as nothing.
3. An arithmetic expression that contains a null evaluates to zero while the concatenation operator is the exception that returns a null result.
4. An arithmetic expression that contains a null evaluates to null while the aggregate functions are the exception that raise an error.