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SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
Guide to SQL: Syntax
The Informix® Guide to SQL: Syntax describes the syntax of the statements, data types, expressions, operators, and built-in functions of the Informix dialect of the SQL language.
Other syntax segments
These 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.
Restrictions on the SELFUNC Modifier
The selectivity function that you specify with the SELFUNC modifier has specific requirements.

SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
- Guide to SQL: Syntax
  The Informix® Guide to SQL: Syntax describes the syntax of the statements, data types, expressions, operators, and built-in functions of the Informix dialect of the SQL language.
  - Overview of SQL syntax
    These topics provide an overview about how to use the SQL statements, SPL statements, and syntax segments.
  - SQL statements
    This chapter describes the syntax and semantics of SQL statements that are recognized by Informix®.
  - SPL statements
    These topics describe Stored Procedure Language (SPL) statements, which you use to write SPL routines. You can store these routines in the database as user-defined routines (UDRs).
  - Data types and expressions
    These topics describe the data types and expressions that Informix®supports.
  - Other syntax segments
    These 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.
    - Arguments
    - Collection-Derived Table
      A collection-derived table is a virtual table in which the values in the rows of the table are equivalent to elements of a collection. Use this segment where you see a reference to Collection-Derived Table in a syntax diagram. This syntax is an extension to the ANSI/ISO standard for SQL.
    - Database Name
    - Database Object Name
    - External Routine Reference
      Include the External Routine Reference clause when you write an external routine. This option is not available for SPL routines.
    - Identifier
      An identifier specifies the unqualified name of a database object, such as an access method, aggregate, alias, blobspace, cast, column, constraint, correlation, data type, index, operator class, partition, procedure, table, trigger, sequence, synonym, or view. Use the Identifier segment whenever you see a reference to an identifier in a syntax diagram.
    - Jar Name
      Use the Jar Name segment to specify the name of a jar ID. Use this segment whenever you see a reference to Jar Name in a syntax diagram.
    - Optimizer Directives
      The Optimizer Directives segment specifies keywords that you can use to partially or fully specify the query plan of the optimizer. Use this segment whenever you see a reference to Optimizer Directives in a syntax diagram.
    - Owner name
      The owner name specifies the owner of a database object. Use this segment whenever you see a reference to Owner Name in a syntax diagram.
    - Purpose Options
    - Return Clause
    - Routine modifier
      A routine modifier specifies characteristics of how a user-defined routine (UDR) behaves.
      - Adding or Modifying a Routine Modifier
        Use this segment in the ALTER FUNCTION, ALTER PROCEDURE, or ALTER ROUTINE statement to add or modify values for routine modifiers of a UDR.
      - Modifier Descriptions
        CLASS
        COSTFUNC (C)
        Use the COSTFUNC modifier to specify the cost of a UDR. The cost of the UDR is an estimate of the time required to execute it.
        HANDLESNULLS
        INTERNAL
        ITERATOR
        NEGATOR
        PARALLELIZABLE
        PERCALL_COST (C)
        Use the PERCALL_COST modifier to specify the approximate CPU usage cost that a UDR incurs each time it executes.
        SELCONST (C)
        Use the SELCONST modifier to specify the selectivity of a UDR. The selectivity of the UDR is an estimate of the fraction of the rows that the query will select.
        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
        Restrictions on the SELFUNC Modifier
        The selectivity function that you specify with the SELFUNC modifier has specific requirements.
        STACK (C)
        VARIANT and NOT VARIANT
    - Routine Parameter List
    - Shared-Object Filename
      Use a shared-object filename to specify a pathname to an executable object file when you register or alter an external routine.
    - Specific Name
    - Statement Block
  - Built-In Routines
  - Appendixes
- Guide to SQL: Reference
  The Informix® Guide to SQL: Reference contains the reference information for the system catalog tables, data types, and environment variables of the HCL Informix dialect of the SQL language, as implemented in HCL Informix. These topics also include information about the stores_demo, sales_demo, and superstore_demo databases that are included with HCL Informix.
- Guide to SQL: Tutorial
  The Informix® Guide to SQL: Tutorial shows how to use basic and advanced structured query language (SQL) to access and manipulate the data in your databases. It discusses the data manipulation language (DML) statements as well as triggers and stored procedure language (SPL) routines, which DML statements often use.

Restrictions on the SELFUNC Modifier

The selectivity function that you specify with the SELFUNC modifier has specific requirements.

The selectivity function that you specify must satisfy the following criteria:

It must take the same number of arguments as the current UDR.
The data type of each argument must be SELFUNCARGS.
It must return a value of type FLOAT between 0 and 1, which represents the percentage of selectivity of the function. (1 is highly selective; 0 is not at all selective.)
It can be written in any language that the database server supports.

A user who invokes the UDR must have the Execute privilege both on that UDR and on the selectivity function that the SELFUNC modifier specifies.

Both the UDR and the selectivity function must have the same owner.

For information on how to use the mi_funcarg* functions to extract information about the arguments of a selectivity function, see the Informix® DataBlade® API Programmer's Guide.