Aggregate functions in PostgreSQL are expressed as state values and state transition functions. That is, an aggregate can be defined in terms of state that is modified whenever an input item is processed. To define a new aggregate function, one selects a data type for the state value, an initial value for the state, and a state transition function. The state transition function is just an ordinary function that could also be used outside the context of the aggregate. A final function can also be specified, in case the desired result of the aggregate is different from the data that needs to be kept in the running state value.

Create a Aggregate

To create a aggregate:

1. Select the Database in the Tree View and select Others > Aggregate from the toolbar
   
2. Press the New Aggregate button
   
3. Enter Aggregate properties and fields on the appropriate tabs of the New Aggregate Editor
4. Click OK

Design a Aggregate

To design a aggregate:

1. Select the Database in the Tree View and select Others > Aggregate from the toolbar
2. Select the aggregate you want to design.
   
3. Press the Design Aggregate button.
   
4. Edit Aggregate properties and fields on the appropriate tabs of the Design Aggregate Editor
5. Click OK
   

Delete a Aggregate

To delete a aggregate:

1. Select the Database in the Tree View and select Others > Aggregate from the toolbar
2. Select the aggregate you want to delete.
   
3. Click the Delete Aggregate button.
4. Confirm deleting in the dialog window.