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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.
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.
Restrictions on Optimizer Directives

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.
      - Optimizer Directives as Comments
        Optimizer directives require valid comment indicators as delimiters.
      - Restrictions on Optimizer Directives
      - Access-Method Directives
        Use the access-method directives to specify the manner in which the optimizer should search the tables.
      - Join-Order Directive
        Use the ORDERED join-order directive to force the optimizer to join tables or views in the order in which they are referenced in the FROM clause of the query.
      - Join-Method Directives
      - Star-Join Directives
      - Optimization-Goal Directives
      - Explain-Mode Directives
      - Statement cache directive
        Use the statement cache directive to prevent the statement from being stored in the statement cache. The AVOID_STMT_CACHE optimizer directive forces the optimizer to reoptimize the statement every time that the statement is run.
      - External Directives
        You can use the SAVE EXTERNAL DIRECTIVES statement to store optimizer directives in the sysdirectives table of the system catalog. Informix® applies these external directives automatically to subsequent queries and subqueries that match a specified SELECT statement.
    - 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.
    - 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 Optimizer Directives

You can specify optimizer directives for any query in a DELETE, SELECT, or UPDATE statement, unless it includes any of the following syntax elements:

A query accessing a table in a database of a remote database server instance
In Informix® ESQL/C, a statement with the WHERE CURRENT OF cursor clause

For queries that use ANSI/ISO-compliant syntax to specify a join, the query optimizer does not follow some directives:

The join-method directives (USE_NL, AVOID_NL, USE_HASH, AVOID_HASH, /BUILD, and /PROBE) are ignored, except in cases where the optimizer rewrites the query so that it is no longer uses the ANSI/ISO syntax.
The join-order directive (ORDERED) is ignored in ANSI-compliant joined queries that specify the RIGHT OUTER JOIN or FULL OUTER JOIN keywords.