Home
SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
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.
Programming for a multiuser environment
Control data modification with access modes

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.
- 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.
  - Database concepts
  - Compose SELECT statements
  - Select data from complex types
  - Functions in SELECT statements
  - Compose advanced SELECT statements
  - Modify data
  - Access and modify data in an external database
  - SQL programming
  - Modify data through SQL programs
  - Programming for a multiuser environment
    - Concurrency and performance
    - Locks and integrity
    - Locks and performance
    - Concurrency issues
    - How locks work
      Informix® database servers support a complex, flexible set of locking features that the topics in this section describe.
    - Lock with the SELECT statement
      The type and duration of locks that the database server places depend on the isolation set in the application and whether the SELECT statement is within an update cursor.
    - Retain update locks
    - Exclusive locks that occur with some SQL statements
      When you execute an INSERT, UPDATE, or DELETE statement, the database server uses exclusive locks. An exclusive lock means that no other users can update or delete the item until the database server removes the lock. In addition, no other users can view the row unless they are using the Dirty Read isolation level.
    - The behavior of the lock types
    - Control data modification with access modes
    - Set the lock mode
    - Simple concurrency
    - Hold cursors
    - The SQL statement cache
    - Summary
  - Create and use SPL routines
  - Create and use triggers

Control data modification with access modes

Informix® database servers support access modes. Access modes affect read and write concurrency for rows within transactions and are set with the SET TRANSACTION statement. You can use access modes to control data modification among shared files.

Transactions are read-write by default. If you specify that a transaction is read-only, that transaction cannot perform the following tasks:

Insert, delete, or update table rows
Create, alter, or drop any database object such as a schema, table, temporary table, index, or stored routine
Grant or revoke privileges
Update statistics
Rename columns or tables

Read-only access mode prohibits updates.

You can execute stored routines in a read-only transaction as long as the routine does not try to perform any restricted operations.

For information about how to use the SET TRANSACTION statement to specify an access mode, see the Informix® Guide to SQL: Syntax.