Which of these SQL functions is used to calculate the number of non-NULL values in a column?

 The SQL function used to calculate the number of non-NULL values in a column is:

COUNT()

By default, COUNT() counts only the non-NULL values in a specified column. Here’s an example of how to use it:

SELECT COUNT(column_name) 
FROM table_name;

This query will return the number of non-NULL values in the column_name of the table_name.

If you want to count all rows, including NULLs, you would use COUNT(*) instead, but for counting non-NULL values specifically, COUNT(column_name) is the correct function.