Strategy Specification
The STRATEGIES keyword introduces a comma-separated list of function names or function signatures for the new operator class. Each element of this list is called a strategy specification and has the following syntax:
Strategy Specification
| Element | Description | Restrictions | Syntax |
|---|---|---|---|
| input_type | Data type of an input parameter to the strategy function for which you intend to use a specific secondary-access method | A strategy function accepts two input parameters and can have one optional output parameter | Data Type |
| output_type | Data type of the optional output parameter of the strategy function | Optional output parameter for side-effect indexes | Data Type |
| strategy_function | Strategy function to associate with the specified operator class | Must be listed in the order that the specified secondary-access method expects | Identifier |
Each strategy_function is an external function. The CREATE
OPCLASS statement does not verify that a user-defined function of
the name you specify exists. However, for the secondary-access method
to use the strategy function, the external function must be:
- Compiled in a shared library
- Registered in the database with the CREATE FUNCTION statement
Optionally, you can specify the signature of a strategy function
in addition to its name. A strategy function requires two input parameters
and an optional output parameter. To specify the function signature,
specify:
- An input data type for each of the two input parameters of the strategy function, in the order that the strategy function uses them
- Optionally, one output data type for an output parameter of the strategy function
You can specify UDTs as well as built-in data types. If you do not specify the function signature, the database server assumes that each strategy function takes two arguments of the same data type and returns a BOOLEAN value.