Welcome
Extending Informix®
Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix includes many built-in extensions that are fully integrated in the database server. Informix also provides modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix.
Creating extensions
You can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
Virtual-Table Interface Guide
The IBM® Informix® Virtual-Table Interface Programmer's Guide explains how to create a primary access method with the Virtual-Table Interface (VTI) so that users have a single SQL interface to HCL Informix tables and to data that does not conform to the storage scheme of HCL Informix.
Descriptor function reference
These topics provide the syntax and usage for the functions that the HCL Informix® database server supplies to access-method developers.
Accessor functions
The Virtual-Table Interface (VTI) library contains functions that primarily access selected fields from the various descriptors.
The mi_qual_column() accessor function
The mi_qual_column() function identifies the key-column argument to a qualification function.

HCL Informix® V15.0.0 documentation
Welcome to the documentation for HCL Informix® 15.0.0 and related client tools and products.
Product overview
HCL Informix® is a fast and scalable database server that manages traditional relational, object-relational, and dimensional databases. Its small footprint and self-managing capabilities are suited to embedded data-management solutions.
Installing
These topics describe how to install HCL Informix® database servers, client products, and modules.
Administering
In addition to administering the database server, you can tune performance, replicate data, and archive data.
Migrating and upgrading
You can upgrade to the 15.0.0 release of HCL Informix® or migrate from other database servers to Informix. Upgrading is an in-place migration method that uses your existing hardware and operating system software. Some changes to the Informix database server can affect upgrading from a previous release.
Client APIs and tools
You can use the HCL Informix® implementation of client APIs to develop applications for Informix database servers.
Embedding Informix®
When you embed HCL Informix®, you can use enterprise-class high-availability and high performance with embeddability features such as easy programmability, a small disk and memory footprint, and silent deployment.
Extending Informix®
Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix includes many built-in extensions that are fully integrated in the database server. Informix also provides modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix.
- Informix® extensions and modules
  These topics describe how to use built-in database extensions and separately installed modules.
- Creating extensions
  You can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
  - Programmer's Guide
    The HCL® Informix® DataBlade® API Programmer's Guide describes information about the , the C-language application programming interface (API) provided with HCL Informix.
  - Function Reference
    The IBM® Informix® DataBlade® API Function Reference describes the functions and the subset of functions that the supports.
  - Developers Kit
    The Developers Kit (DBDK) guides contain information about the tools you can use to develop and package modules, which extend the functionality of HCL Informix® databases.
  - J/Foundation Developer's Guide
    The HCL® J/Foundation Developer's Guide describes how to write user-defined routines (UDRs) in the Java™ programming language for Informix®.
  - R-Tree Index User's Guide
    The HCL® Informix® R-Tree Index User's Guide describes the HCL Informix R-tree secondary access method and how to access and use its components.
  - User-Defined Routines and Data Types Developer's Guide
    The HCL® Informix® User-Defined Routines and Data Types Developer's Guide describes how to define new data types and enable user-defined routines (UDRs) to extend HCL Informix.
  - Virtual-Table Interface Guide
    The IBM® Informix® Virtual-Table Interface Programmer's Guide explains how to create a primary access method with the Virtual-Table Interface (VTI) so that users have a single SQL interface to HCL Informix tables and to data that does not conform to the storage scheme of HCL Informix.
    - Access methods
      This section describes access methods, explains why you create user-defined access methods, and shows you how to create user-defined access methods
    - Develop an access method
      These topics describe the steps that you take to implement a user-defined access method with the Virtual-Table Interface (VTI).
    - Design decisions
      These topics present the choices that you make to optimize the performance and flexibility of the access method that you can create with the virtual-table interface (VTI).
    - Purpose-function reference
      These topics describe the purpose functions that the access-method developer provides.
    - Descriptor function reference
      These topics provide the syntax and usage for the functions that the HCL Informix® database server supplies to access-method developers.
      - Descriptor reference
        Descriptors are the predefined data structures through which the database server and access method pass information.
      - Accessor functions
        The Virtual-Table Interface (VTI) library contains functions that primarily access selected fields from the various descriptors.
        The mi_eval_am_qual() accessor function
        The mi_eval_am_qual() function evaluates parts of a qualification that the access method does not set to MI_VALUE_TRUE or MI_VALUE_FALSE.
        The mi_init_am_qual() accessor function
        The mi_init_am_qual() function reinitializes all parts of the qualification to MI_VALUE_NOT_EVALUATED.
        The mi_qual_boolop() accessor function
        The mi_qual_boolop() function retrieves the Boolean operator that combines two qualifications in a complex expression.
        The mi_qual_column() accessor function
        The mi_qual_column() function identifies the key-column argument to a qualification function.
        The mi_qual_commuteargs() accessor function
        The mi_qual_commuteargs() function determines whether the constant precedes the column in a qualification-function argument list.
        The mi_qual_constant() accessor function
        The mi_qual_constant() function retrieves the constant value that the WHERE clause specifies as a qualification-function argument.
        The mi_qual_constant_nohostvar() accessor function
        The mi_qual_constant_nohostvar() function returns an explicit constant value, if any, from the qualification-function arguments.
        The mi_qual_constant_typeid() accessor function
        The mi_qual_constant_typeid() function returns the data type of the constant.
        The mi_qual_constisnull() accessor function
        The mi_qual_constisnull() function determines whether the arguments to a qualification function include a NULL constant.
        The mi_qual_constisnull_nohostvar() accessor function
        The mi_qual_constisnull_nohostvar() function determines whether a qualification-function argument list contains an explicit NULL value.
        The mi_qual_const_depends_hostvar() accessor function
        The mi_qual_const_depends_hostvar() function indicates whether the value of a host variable influences the evaluation of a qualification.
        The mi_qual_const_depends_outer() accessor function
        The mi_qual_const_depends_outer() function indicates that an outer join provides the constant in a qualification.
        The mi_qual_funcid() accessor function
        The mi_qual_funcid() function returns the routine identifier of a qualification function.
        The mi_qual_funcname() accessor function
        The mi_qual_funcname() function returns the name of a qualification function.
        The mi_qual_handlenull() accessor function
        The mi_qual_handlenull() function determines whether the qualification function can accept NULL arguments.
        The mi_qual_issimple() accessor function
        The mi_qual_issimple() function determines whether a qualification is a function.
        The mi_qual_needoutput() accessor function
        The mi_qual_needoutput() function determines whether the access method must set the value for an OUT argument in a UDR.
        The mi_qual_negate() accessor function
        The mi_qual_negate() function indicates whether the NOT Boolean operator applies to the results of the specified qualification. The NOT operator can negate the return value of a function or a Boolean expression.
        The mi_qual_nparams() accessor function
        The mi_qual_nparams() function retrieves the number of parameters in the qualification expression.
        The mi_qual_nquals() accessor function
        The mi_qual_nquals() function retrieves the number of qualifications in an AND or OR qualification expression.
        The mi_qual_qual() accessor function
        The mi_qual_qual() function points to one function or Boolean expression in a complex qualification.
        The mi_qual_setoutput() accessor function
        The mi_qual_setoutput() function sets a constant-argument value for a UDR.
        The mi_qual_setreopt() accessor function
        The mi_qual_setreopt() function sets an indicator in the qualification descriptor to force reoptimization.
        The mi_qual_setvalue() accessor function
        The mi_qual_setvalue() function sets a qualification result.
        The mi_qual_value() accessor function
        The mi_qual_value() function retrieves the result of a qualification.
        The mi_qual_param() accessor function
        The mi_qual_param() function returns the parameter descriptor for the specified parameter.
        The mi_qual_param_column() accessor function
        The mi_qual_param_column() function retrieves the column number in the virtual table that is associated with the specified parameter.
        The mi_qual_param_constant() accessor function
        The mi_qual_param_constant() function retrieves the constant value for the specified parameter.
        The mi_qual_param_constant_typeid() accessor function
        The mi_qual_param_constant_typeid() function returns the data type of the constant.
        The mi_qual_param_constisnull() accessor function
        The mi_qual_param_constisnull() function determines whether the arguments to a qualification function include a NULL constant.
        The mi_qual_param_expression() accessor function
        The mi_qual_param_expression() function returns the qualifier descriptor for the parameter, which is an expression.
        The mi_qual_param_iscolumn() accessor function
        The mi_qual_param_iscolumn() function determines whether a parameter is a column.
        The mi_qual_param_isconstant() accessor function
        The mi_qual_param_isconstant() function determines whether a parameter is a literal value.
        The mi_qual_param_isexpression() accessor function
        The mi_qual_param_isexpression() function determines whether a parameter is an expression.
        The mi_qual_param_issimple() accessor function
        The mi_qual_param_issimple() function determines whether a parameter is either a column or literal value, or an expression.
        The mi_scan_forupdate() accessor function
        The mi_scan_forupdate() function determines if the SELECT query includes a FOR UPDATE clause.
        The mi_scan_isolevel() accessor function
        The mi_scan_isolevel() function retrieves the isolation level that the database server expects for the table that am_getnext scans.
        The mi_scan_locktype() accessor function
        The mi_scan_locktype() function retrieves the lock type that the database server expects for the table that am_getnext scans.
        The mi_scan_newquals() accessor function
        The mi_scan_newquals() function indicates whether the qualification descriptor includes changes between multiple scans for the same query statement.
        The mi_scan_nprojs() accessor function
        The mi_scan_nprojs() function returns a value that is 1 less than the number of columns in a query projection.
        The mi_scan_projs() accessor function
        The mi_scan_projs() function identifies each column that the Projection clause of a query specifies.
        The mi_scan_quals() accessor function
        The mi_scan_quals() function returns the qualification descriptor, which describes the conditions that an entry must satisfy to qualify for selection.
        The mi_scan_setuserdata() accessor function
        The mi_scan_setuserdata() function stores a pointer to user data in the scan descriptor.
        The mi_scan_table() accessor function
        The mi_scan_table() function retrieves a pointer to the table descriptor for the table that the access method scans.
        The mi_scan_userdata() accessor function
        The mi_scan_userdata() function retrieves the pointer from the scan descriptor that points to a user data structure.
        The mi_tab_amparam() accessor function
        The mi_tab_amparam() function retrieves any user-defined configuration values for the table.
        The mi_tab_check_msg() function
        The mi_tab_check_msg() function sends messages to the oncheck utility.
        The mi_tab_createdate() accessor function
        The mi_tab_createdate() function returns the date that the table was created.
        The mi_tab_id() accessor function
        The mi_tab_id() function retrieves the table identifier from the table descriptor.
        The mi_tab_isolevel() accessor function
        The mi_tab_isolevel() function retrieves the isolation level that the SET ISOLATION or SET TRANSACTION statement applies.
        The mi_tab_istable() accessor function
        The mi_tab_istable() function indicates whether the table descriptor describes a table.
        The mi_tab_mode() accessor function
        The mi_tab_mode() function retrieves the I/O mode of the table from the table descriptor.
        The mi_tab_name() accessor function
        The mi_tab_name() function retrieves the table name that the active SQL statement or oncheck command specifies.
        The mi_tab_niorows() accessor function
        The mi_tab_niorows() function retrieves the number of rows that the database server expects to process in am_getnext.
        The mi_tab_numfrags() accessor function
        The mi_tab_numfrags() function retrieves the number of fragments in the table.
        The mi_tab_owner() accessor function
        The mi_tab_owner() function retrieves the owner of the table.
        The mi_tab_partnum() accessor function
        The mi_tab_partnum() function retrieves the fragment identifier for the table.
        The mi_tab_rowdesc() accessor function
        The mi_tab_rowdesc() function retrieves the row descriptor, which describes the columns that belong to the table that the table descriptor identifies.
        The mi_tab_setnextrow() accessor function
        The am_getnext purpose function calls mi_tab_setnextrow() to store the next entry that qualifies for selection.
        The mi_tab_setniorows() accessor function
        The mi_tab_setniorows() function indicates that the access method can handle more than one row per call and the number of rows for which the database server should allocate memory.
        The mi_tab_setuserdata() accessor function
        The mi_tab_setuserdata() function stores a pointer to user data in the table descriptor.
        The mi_tab_spaceloc() accessor function
        The mi_tab_spaceloc() function retrieves the location of the extspace in which the table resides.
        The mi_tab_spacename() accessor function
        The mi_tab_spacename() function retrieves the name of the storage space where the virtual table resides.
        The mi_tab_spacetype() accessor function
        The mi_tab_spacetype() function retrieves the type of storage space in which the virtual table resides.
        The mi_tab_update_stat_mode() accessor function
        The mi_tab_update_stat_mode() function indicates whether an UPDATE STATISTICS function includes a LOW, MEDIUM, or HIGH mode keyword.
        The mi_tab_userdata() accessor function
        The mi_tab_userdata() function retrieves, from the table descriptor, a pointer to a user-data structure that the access method maintains in shared memory.
        The mi_tstats_setnpages() accessor function
        The mi_tstats_setnpages() function stores the number of table pages in the statistics descriptor.
        The mi_tstats_setnrows() accessor function
        The mi_tstats_setnrows() function stores the number of table rows in the statistics descriptor.
    - SQL statements for access methods
      These topics describe the syntax and usage of the ALTER ACCESS_METHOD, CREATE PRIMARY ACCESS_METHOD, and DROP ACCESS_METHOD statements, which insert, change, or delete entries in the sysams system catalog table.
    - XA-compliant external data sources
      The HCL Informix® Transaction Manager recognizes XA-compliant external data sources, which can participate in two-phase commit transactions.
  - Virtual-Index Interface Guide
    The IBM® Informix® Virtual-Index Interface Programmer's Guide explains how to create a secondary access method with the Virtual-Index Interface (VII) to extend the built-in indexing schemes of HCL Informix typically with a module.
Data warehousing
In addition to designing and implementing Informix® dimensional databases, you can use tools to create data warehouse applications and optimize your data warehouse queries.
Designing databases
The first step in creating a relational database is to construct a data model, which is a precise, complete definition of the data you want to store. After you prepare your data model, you must implement it as a database and tables. To implement your data model, you first select a data type for each column and then you create a database and tables and populate the tables with data. You can also implement fragmentation strategies and control access to your data.
JSON compatibility
You can use the popular JSON-oriented query language created by MongoDB to interact with data stored in HCL Informix®.
Security
You can secure your Informix® database server and the data that is stored in your Informix databases. You can encrypt data, secure connections, control user privileges and access, and audit data security.
SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
Troubleshooting HCL Informix®
Several troubleshooting techniques, tools, and resources are available for resolving problems that you encounter in your HCL Informix® database server environment.

The mi_qual_column() accessor function

The mi_qual_column() function identifies the key-column argument to a qualification function.

Syntax

mi_smallint mi_qual_column(MI_AM_QUAL_DESC *qualDesc);

qualDesc: Points to the qualification descriptor.

Usage

A qualification identifies a column by a number that locates the column in the row descriptor. The mi_qual_column() function returns the number 0 for the first column specified in the row descriptor and adds 1 for each subsequent column.

For example, assume that the WHERE clause contains the function equal(name,'harry') and that name is the second column in the row. The mi_qual_column() function returns the value 1.

The access method might need to identify the column by name, for example, to assemble a query for an external database manager. To retrieve the column name, pass the return value of mi_qual_column() and the row descriptor to the mi_column_name() function as in the following example:

rowDesc = mi_tab_rowdesc(tableDesc);
colnum=mi_qual_column(qualDesc);
colname=mi_column_name(rowDesc,colnum);

Return values

The integer identifies the column argument by its position in the table row.

Related topics

See the description of:

row-descriptor accessor functions in the HCL® Informix® DataBlade® API Programmer's Guide