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SQL programmingYou can use the HCL OneDB™ implementation of the SQL language to develop applications for HCL OneDB™ database servers.
Guide to SQL: SyntaxThe HCL OneDB™ Guide to SQL: Syntax describes the syntax of the statements, data types, expressions, operators, and built-in functions of the HCL OneDB™ dialect of the SQL language.
Other syntax segmentsThese topics describe syntax segments, which are language elements, such as database object names or optimizer directives, that appear as a subdiagram reference in the syntax diagrams of some SQL or SPL statements.
Routine modifier A routine modifier specifies characteristics of how a user-defined routine (UDR) behaves.
Modifier Descriptions
SELFUNC (C)Use the SELFUNC modifier with a C UDR to name a companion user-defined function, called a selectivity function, to the current UDR. The selectivity function provides selectivity information about the current UDR to the optimizer.
Concept of Selectivity

Concept of Selectivity

Selectivity is an attribute of queries that performs a search based on an equality condition. The selectivity of the query depends inversely on the proportion of qualifying rows. The smaller the proportion of qualifying rows among all the rows in FROM clause table objects, the more selective is the query.

For example, the following query has a search condition based on the customer_num column in the customer table:

SELECT * FROM customer WHERE customer_num = 102;

Because each row in the table has a different customer number, this query is highly selective. In contrast, the following query has low selectivity:

SELECT * FROM customer WHERE state = 'CA';

Because most of the rows in the customer table are for customers in California, more than half of the rows in the table would be returned.

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