Oracle and DB2, Comparison and Compatibility/Storage Model/Data Types/Summary
Summary[edit | edit source]
Oracle and DB2 Data Type Comparison Matrix
In this matrix, each data type described for Oracle is listed in the left hand column, and is paired with its DB2 equivalent in the right hand column. Where DB2 has a number of named data types that equate to a single Oracle data type (for example in Numeric Data Types), the related Oracle data type is shown duplicated but with a precision and scale that equal the DB2 data type. If there is no equivalence, the data type is left blank and a mention is made in the Description. The net is that for each data type previously identified for Oracle and DB2 there is an entry in the following matrix.
- Oracle has the built-in SQL functions DBTIMEZONE and SESSIONTIMEZONE that you can query to verify the database and session time zones. If the database time zone or the session time zone has not been set manually, Oracle Database uses the operating system time zone
DB2 has a series of special registers that are storage areas that can be referenced in SQL statements. CURRENT TIMEZONE specifies the TIMEZONE parameter in the form of a time duration with a data type of DECIMAL(6,0) in the format HHMMSS. The time duration is derived by the instance that executes the SQL statement. To get the CURRENT TIME or CURRENT TIMESTAMP adjusted to GMT/UTC, subtract the CURRENT TIMEZONE register from the CURRENT TIME or TIMESTAMP.
The assumption is that the clock is set to local time and the TIMEZONE parameter is zero, or the clock is set to GMT and the TIMEZONE parameter gives the difference from GMT.
The net of this is that TIMESTAMP, TIMESTAMP WITH TIMEZONE and TIMESTAMP WITH LOCAL TIMEZONE are all really the same thing. They are a timestamp with the format YYYY / MM / DD / HH:MM:SS:FFFFFF that is adjusted based on the setting of the clock on the server of the database instance, AND the value of a register (DB2) or built-in function (Oracle). It’s just something you need to pay attention to in conversion/compatibility. What are the settings where you are, and what are the settings where you are going.
Because of how DB2 points to rows within a page, the ROWID points to the page that contains the row. Where the actual row exists in the page is handled by pointers (since a row can move around in a page, and it’s offset is stored in the ID Map at the bottom of the page), so the ROWID will get you to the DB2 page, and then it’s ID Map will get you to the row. In Oracle, the ROWID points to the row location in the block, and if that location is a pointer to another block, this is a relative address (UROWID).
- SQL statements that create tables and clusters can also use ANSI and DB2 data types. Oracle provides the XMLType datatype to handle XML data. Oracle will recognize the ANSI or DB2 data type name and use this as the name of the data type of the column. The actual data is stored as an Oracle native data type. XML data stored in DB2 is stored in the UTF-8 code set. XML values are stored in an internal representation that is not a string and is not directly comparable to string values.