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 the DB2 product.
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
Any unqualified reference to the DUAL table is resolved
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.
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.
Synonym usage You can set the DB2_COMPATIBILITY_VECTOR registry variable to restrict the use of synonyms.
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.