### Question

When do we use the COUNT() function or the SUM() function?

### Answer

Although they might appear to perform a similar task, the `COUNT()`

and `SUM()`

functions have very different uses.

`COUNT()`

is used to take a name of a column, and counts the number of non-empty values in that column. `COUNT()`

does not take into account the actual values stored, and only cares if they have a non-empty value. Each row is essentially counted as `1`

towards the total count.

On the other hand, `SUM()`

takes a column name, and returns the sum of all values in the column, meaning that it must take into account the actual values stored.

In general, use `COUNT()`

when you want to count how many rows contain a non-empty value for a specified column. Use `SUM()`

when you want to get the total sum of all values in a column.