フリー問題

問題文

One column holds NULL in some rows. How does COUNT over that column differ from COUNT with the asterisk?

選択肢

1. The column form counts the populated values inside that column, and the asterisk form counts the grouped keys regardless of the missing entries.
2. The column form counts the distinct labels inside that column, and the asterisk form counts the grouped keys regardless of the missing entries.
3. The column form counts the distinct labels inside that column, and the asterisk form counts the returned rows regardless of the missing entries.
4. The column form counts the populated values inside that column, and the asterisk form counts the returned rows regardless of the missing entries.