Home
SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
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.
Data types
Every column in a table in a database is assigned a data type. The data type precisely defines the kinds of values that you can store in that column.
Extended Data Types
Opaque Data Types
An opaque data type is a user-defined or built-in data type that is fully encapsulated. The internal structure of an opaque data type is unknown to the database server.

SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
- Guide to SQL: Syntax
- 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.
  - System catalog tables
    The system catalog consists of tables and views that describe the structure of the database. Sometimes called the data dictionary, these table objects contain everything that the database knows about itself. Each system catalog table contains information about specific elements in the database. Each database has its own system catalog.
  - Data types
    Every column in a table in a database is assigned a data type. The data type precisely defines the kinds of values that you can store in that column.
    - Summary of data types
      HCL Informix® supports the most common set of built-in data types. Additionally, an extended set of data types are supported on the database server.
    - ANSI to Informix data type mapping
    - Description of Data Types
    - Built-In Data Types
    - Extended Data Types
      - Complex data types
        A complex data type can store one or more values of other built-in or extended data types.
      - Distinct Data Types
        A distinct data type has the same internal structure as some other source data type in the database. The source type can be a built-in or extended data type. What distinguishes a distinct type from its source type are support functions that are defined on the distinct type.
      - Opaque Data Types
        An opaque data type is a user-defined or built-in data type that is fully encapsulated. The internal structure of an opaque data type is unknown to the database server.
    - Data Type Casting and Conversion
    - Operator Precedence
  - Environment variables
    Various environment variables affect the functionality of your HCL Informix® products. You can set environment variables that identify your terminal, specify the location of your software and define other parameters.
  - Appendixes
- 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.

Opaque Data Types

An opaque data type is a user-defined or built-in data type that is fully encapsulated. The internal structure of an opaque data type is unknown to the database server.

Except for user-defined types (UDTs) that are DISTINCT of built-in non-opaque types, UDTs whose source types are built-in types are opaque data types. Similarly, UDTs that are DISTINCT of built-in opaque types are opaque types.

Built-in opaque data types

The built-in data types BLOB, BOOLEAN, CLOB, BSON, JSON, and LVARCHAR are implemented as opaque data types. You can access all of these in other databases of the same Informix® instance, but you cannot access the BLOB or CLOB built-in opaque data types in cross-server distributed operations.

UDTs that are DISTINCT of built-in opaque types and that are cast to built-in types are valid in cross-server queries and other DML operations, but all the casts and all the DISTINCT OF definitions for the UDTs must be identical in every participating database.

Several system catalog tables, whose schema are shown in Structure of the System Catalog, have columns of built-in opaque data types. For information on how the system catalog emcodes columns of built-in opaque data types, see SYSCOLUMNS.

User-defined opaque data types

You must provide the following information to the database server for an opaque data type:

A data structure for how the data values are stored on disk
Support functions to determine how to convert between the disk storage format and the user format for data entry and display
Secondary access methods that determine how the index on this data type is built, used, and manipulated
User functions that use the data type
A system catalog entry to register the opaque type in the database

The internal structure of an opaque type is not visible to the database server and can only be accessed through user-defined routines. Definitions for opaque types are stored in the sysxtdtypes system catalog table. These SQL statements maintain the definitions of opaque types in the database:

The CREATE OPAQUE TYPE statement registers a new opaque type in the database.
The DROP TYPE statement removes a previously defined opaque type from the database.

For more information, see the section OPAQUE data types. See also Informix® User-Defined Routines and Data Types Developer's Guide.