A diary of some sort. An interesting one.

An aggregate function allows one perform a calculation on a set of values to return a single scalar value. Commonly used ones include:

`COUNT()`

=> number of rows with non-empty values`SUM()`

=> sum of all values in a column`MAX()`

/`MIN()`

`AVG()`

`ROUND()`

=> e.g. –`ROUND(columnName, decimalPlaces)`

`GROUP BY`

=> groups identical data into groups`HAVING`

=> limits result of a query based on aggregate property.