Which statement counts only non-null values in a column?

Which statement counts only non-null values in a column?

• A. SELECT COUNT(*) FROM table;
• B. SELECT COUNT(column_name) FROM table;
• C. SELECT SUM(column_name) FROM table;
• D. SELECT COUNT(DISTINCT column_name) FROM table;

Answer: (B)

Counting non-null values in a column focuses on how many rows actually have data in that column. The statement uses a function that increments only when the column value is not NULL, so you get the number of rows that contain a real value. This is why it’s the best choice for counting how many entries exist in that column with data. In contrast, counting all rows will include those with NULLs, giving a larger total that doesn’t reflect how many entries actually hold data in that column. For reference, if you want to count distinct non-null values, you’d use a different form, and for summing numbers you’d use a sum function, which handles NULLs in its own way but serves a different goal.

Counting non-null values in a column focuses on how many rows actually have data in that column. The statement uses a function that increments only when the column value is not NULL, so you get the number of rows that contain a real value. This is why it’s the best choice for counting how many entries exist in that column with data. In contrast, counting all rows will include those with NULLs, giving a larger total that doesn’t reflect how many entries actually hold data in that column. For reference, if you want to count distinct non-null values, you’d use a different form, and for summing numbers you’d use a sum function, which handles NULLs in its own way but serves a different goal.