The following table summarizes the tasks that a C UDR can perform. It also describes where you can find additional information in this manual for each of these UDR uses.
| Type of UDR | Purpose | More Information |
|---|---|---|
| Cast function | A UDR that converts one data type to another | Writing a Cast Function |
| Cost function | A UDR that determines the cost of execution for an expensive UDR | Writing Selectivity and Cost Functions |
| End-user routine | A UDR that performs some common task for an end user | Writing an End-User Routine |
| Iterator function | A function that returns more than one row of data | Writing an Iterator Function |
| Opaque-type support function | One of a group of user-defined functions that tell the database server how to handle the data of an opaque data type | Creating an Opaque Data Type |
| Operator-class function | User-defined functions that define operators to use with a particular secondary access method | See your access-method documentation. |
| Negator function | A user-defined function that calculates the Boolean NOT operation for a particular operator or function. | Creating Negator Functions |
| Selectivity function | A UDR that determines the percentage of rows likely to be returned by an expensive UDR | Writing Selectivity and Cost Functions |
| Parallelizable UDR | A UDR that can run in parallel when executed within a PDQ statement | Creating Parallelizable UDRs |
| User-defined aggregate | A function that calculates an aggregate value on a particular column or value | Writing an Aggregate Function |