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Apache Derby 10.4 | ||||||||
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See:
Description
| Interface Summary | |
|---|---|
| VTICosting | VTICosting is the interface that the query optimizer uses to cost Table Functions. |
| VTIEnvironment | VTIEnvironment is the state variable created by the optimizer to help it place a Table Function in the join order. |
Derby lets you declare functions which return ResultSets. You can then use these function results as tables in your queries. This, in turn, lets you do the following:
Here is an example of how to declare and invoke a Table Function:
CREATE FUNCTION externalEmployees
()
RETURNS TABLE
(
employeeId INT,
lastName VARCHAR( 50 ),
firstName VARCHAR( 50 ),
birthday DATE
)
LANGUAGE JAVA
PARAMETER STYLE DERBY_JDBC_RESULT_SET
NO SQL
EXTERNAL NAME 'com.acme.hrSchema.EmployeesTable.read'
;
INSERT INTO employees
SELECT s.*
FROM TABLE (externalEmployees() ) s;
The Derby optimizer makes some assumptions about these Table Functions:
Based on these assumptions, the optimizer decides where to place the Table Function in the join order. Using the interfaces in this package, you may override the optimizer's guesses and force the optimizer to choose a better join order.
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Built on Wed 2008-04-16 18:34:32+0200, from revision 648739 | ||||||||
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