Answer: SELECT count_if(member_id IS NULL) FROM my_table;

## Explanation **Option C (`SELECT count_if(member_id IS NULL) FROM my_table;`)** is the correct answer because: 1. **`count_if()` function** in Databricks SQL is specifically designed to count rows that satisfy a given condition. 2. **`member_id IS NULL`** is the correct condition to identify null values in the column. 3. The `count_if()` function returns the number of rows where the condition evaluates to true. **Why other options are incorrect:** - **Option A (`SELECT count(member_id) FROM my_table;`)**: The `count()` function counts only non-null values. According to the Databricks documentation, when a column is specified (not `*`), `count()` only counts rows where the expression is not NULL. - **Option B (`SELECT count(member_id) - count_null(member_id) FROM my_table;`)**: There is no built-in `count_null()` function in Databricks SQL. This would result in an error. - **Option D (`SELECT null(member_id) FROM my_table;`)**: The `null()` function doesn't exist for counting null values. This would either return null values or result in an error. - **Option E (`SELECT count_null(member_id) FROM my_table;`)**: As mentioned, there is no `count_null()` function in Databricks SQL. This is not a valid SQL function. **Key Learning Points:** - Use `count_if(column IS NULL)` to count null values in a column - `count(column)` counts only non-null values - `count(*)` counts all rows including those with null values - Always refer to official Databricks documentation for function behavior

Author: Keng Suppaseth