Provide UDR-optimization functions

The DataBlade® API provides support for you to create the following kinds of special-purpose UDRs to optimize UDR performance:

Tasks that optimize execution of UDRs
When you write a UDR, you can provide the query optimizer with the following information to help it determine the best query path for queries that contain the UDR.

Filter optimization More information

Parallel Execution Creating parallelizable UDRs

Cost-of-execution Query cost
UDRs that optimize query filters

Filter optimization	More information
Parallel Execution	Creating parallelizable UDRs
Cost-of-execution	Query cost

If your UDR returns a BOOLEAN value (mi_boolean), it is called a Boolean function. The following table shows the kinds of Boolean functions that are useful as filters in a query.

Table 1. Boolean functions useful as query filters
Comparison condition	Operator symbol	Associated user-defined function
Relational operator	=, !=, <> <, <= >, >=	equal(), notequal(), notequal() lessthan(), lessthanorequal() greaterthan(), greaterthanorequal()
LIKE, MATCHES	None	like(), matches()
Boolean function	None	Name of a user-defined function that returns a BOOLEAN value

When you write one of the Boolean functions in Boolean functions useful as query filters, you can also provide the query optimizer with information about how to best evaluate a filter that consists of the Boolean function. You can define the following UDR-optimization functions for Boolean functions.


Filter optimization	More information
Negator function	implementing a negator function with a C user-defined function
Selectivity	Query selectivity