TAILIEUCHUNG - ORACLE8i- P7

ORACLE8i- P7: We want information information.” Possibly you recognize these words as the primary interest of a somewhat clandestine group, and as told by a character called Number 2 to Patrick McGoohan’s character Number 6 (in the old TV show The Prisoner). Indeed, in this day, information is king, and the speedy, accurate, and reliable retrieval of this information is paramount. | 230 CHAPTER 6 ORACLE SCHEMA OBJECT MANAGEMENT addition of Oracle objects and partitioning the format of the native database ROWID needed to be expanded and the extended ROWID was born. Let s look at each of these ROWID types in a bit more detail. Extended ROWIDs The extended ROWID is the native form of a ROWID in Oracle8i and was first introduced with Oracle8. Extended ROWIDs are relative only to a given tablespace. This is different from the relative ROWID that was present in Oracle7 which made every row in the database unique throughout the entire database. The extended ROWID is an 18-character value that represents four different values Data object number This is a six-character representation of a 32-bit data object number. This number uniquely identifies the database segment. Each time an object changes the data object number associated with this object changes as well. Thus the data object number also serves as a version number for the object. Relative datafile number This is a three-character representation of the relative datafile number. The relative datafile number is relative to the tablespace to which that tablespace belongs. Thus objects in different tablespaces will likely have different relative datafile numbers. Data block This is a six-character representation of the data block. This block number is relative to the tablespace to which it belongs. Row number in the block This is a three-character representation of the row in the block. An example of an extended ROWID is shown in the query below. SQL SELECT rowid FROM test ROWID AAAAx AABAAADhBAAA AAAAx AABAAADhBAAB AAAAx AABAAADhBAAC AAAAx AABAAADhBAAD As you can see the ROWID is a rather odd-looking thing. All of the different letters do not translate into anything usable by the DBA except that they can be used directly in a SQL statement s WHERE clause in certain cases for example if you store ROWIDs in a table . To effectively use an extended ROWID you will probably need to employ the Oracle .

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