Which clause is used with an "aggregate functions"?

This question asks about aggregate functions in MySQL. Aggregate functions are special functions that summarize data in a table, like calculating the average, sum, or count of values.

Now, let's look at the options:

Option A: GROUP BY
The GROUP BY clause is used to group rows with similar values together before applying an aggregate function. So, this option is a good possibility.

Option B: SELECT
The SELECT clause is used to choose which columns you want to see in your result set. While you can use aggregate functions within a SELECT statement, the SELECT clause itself doesn't directly work with grouping.

Option C: WHERE
The WHERE clause filters rows based on certain conditions. It helps select specific data but doesn't directly handle grouping.

Option D: Both GROUP BY and WHERE
This option combines both GROUP BY and WHERE. While you can use WHERE to filter data before grouping, the actual grouping is done by GROUP BY.

Therefore, the correct answer is Option A: GROUP BY .