DB2 Version 10.1 for Linux, UNIX, and Windows

DB2 compatibility features

DB2 compatibility features introduction
The DB2® product provides a number of features that reduce the time and complexity of enabling some applications that were written for relational database products other than the DB2 product to run on a DB2 system.
DB2_COMPATIBILITY_VECTOR registry variable
The DB2_COMPATIBILITY_VECTOR registry variable enables one or more DB2 compatibility features. These features ease the task of migrating applications that were written for relational database products other than the DB2 product to DB2 Version 9.5 or later.
Setting up the DB2 environment for Oracle application enablement
You can reduce the time and complexity of enabling Oracle applications to work with DB2 data servers if you set up the DB2 environment appropriately.
Data types
Character and graphic constant handling
Implicit casting (or weak typing) is an alternative way to parse character or graphic constants to support applications that expect these constants to be assigned the data types CHAR and GRAPHIC.
SQL data-access-level enforcement
The degree to which a routine (stored procedure or user-defined function) can execute SQL statements is determined by its SQL-access-level.
Outer join operator
When you set the DB2_COMPATIBILITY_VECTOR registry variable to support the outer join operator (+), queries can use this operator as alternative syntax within predicates of the WHERE clause.
Hierarchical queries
A hierarchical query is a form of recursive query that retrieves a hierarchy, such as a bill of materials, from relational data by using a CONNECT BY clause.
Compatibility database configuration parameters
You can use database configuration parameters to indicate whether the compatibility semantics associated with the certain data types are applied to the connected database.
ROWNUM pseudocolumn
Any unresolved and unqualified column reference to the ROWNUM pseudocolumn is converted to the OLAP specification ROW_NUMBER() OVER().
DUAL table
The DB2 data server resolves any unqualified reference to the DUAL table as a built-in view that returns one row and one column that is named DUMMY, whose value is 'X'.
Insensitive cursor
You can make cursors insensitive to subsequent statements by materializing the cursor at OPEN time. Statements that are executed while the cursor is open do not affect the result table once all the rows have been materialized in the temporary copy of the result table.
INOUT parameters
You can define the INOUT parameter for a procedure to have a default value, by using the DEFAULT keyword.
Currently committed semantics improve concurrency
Oracle data dictionary-compatible views
When you set the DB2_COMPATIBILITY_VECTOR registry variable to support Oracle data dictionary-compatible views, the views are automatically created when you create a database.
Oracle database link syntax
When you set the DB2_COMPATIBILITY_VECTOR registry variable to support Oracle database link syntax, you can connect with a remote database, table, or view.
Terminology mapping: Oracle to DB2 products
Because Oracle applications can be enabled to work with DB2 data servers when the DB2 environment is set up appropriately, it is important to understand how certain Oracle concepts map to DB2 concepts.