mozIStorageAggregateFunction represents aggregate SQL function.
Common examples of aggregate functions are SUM() and COUNT().
An aggregate function calculates one result for a given set of data, where
a set of data is a group of tuples. There can be one group
per request or many of them, if GROUP BY clause is used or not.
onStep is called when next value should be passed to
a custom function.
| aFunctionArguments | The arguments passed in to the function |
Called when all tuples in a group have been processed and the engine
needs the aggregate function’s value.
| aggregate result as Variant. |