Oracle Built−in Packages- P90 pdf

In Oracle8, then, a ROWID contains the following information: • The data object number • The data file where the first file is 1 • The data block within the data file • The row in the da

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9.1.1.3 DBMS_ROWID nonprogram elements

Table 9.3 lists the named constants defined by the DBMS_ROWID package for use with its programs

Table 9.3: DBMS_ROWID Constants

ROWID_TYPE_RESTRICTED A ROWID type: integer constant assigned the value of 0

ROWID_TYPE_EXTENDED A ROWID type: integer constant assigned the value of 1

ROWID_IS_VALID A ROWID verification result: integer constant assigned the value of 0 ROWID_IS_INVALID A ROWID verification result: integer constant assigned the value of 1 ROWID_OBJECT_UNDEFINED An object type indicating that the object number is not defined (for

restricted ROWIDs): integer constant assigned the value of 0

ROWID_CONVERT_INTERNAL A ROWID conversion type: integer constant assigned the value of 0 ROWID_CONVERT_EXTERNAL A ROWID conversion type: integer constant assigned the value of 1

9.1.2 ROWID Concepts

This section offers a quick overview of the Oracle ROWID You can get much more extensive information on ROWIDs from the Oracle documentation

In the Oracle RDBMS, ROWID is a pseudocolumn that is a part of every table you create The ROWID is an internally generated and maintained binary value that identifies a row of data in your table It is called a pseudocolumn because a SQL statement includes it in places where you would normally use a column

However, it is not a column that you create for the table Instead, the RDBMS generates the ROWID for each row as it is inserted into the database The information in the ROWID provides the exact physical location of the row in the database You cannot change the value of a ROWID

You can use the ROWID datatype to store ROWIDs from the database in your PL/SQL program You can SELECT or FETCH the ROWID for a row into a ROWID variable To manipulate ROWIDs in Oracle8, you will want to use the DBMS_ROWID package described in this chapter In Oracle7, you will use the

ROWIDTOCHAR function to convert the ROWID to a fixed−length string and then perform operations against that string

In Oracle7, the format of the fixed−length ROWID is,

BBBBBBB.RRRR.FFFFF

where components of this format have the following meanings:

BBBBBBB

The block in the database file

RRRR

The row in the block (where the first row is zero, not one)

FFFFF

The database file

All these numbers are hexadecimal; the database file is a number that you would then use to look up the actual name of the database file through the data dictionary

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In Oracle8, ROWIDs have been "extended" to support partitioned tables and indexes The new, extended ROWIDs include a data object number, identifying the database segment Any schema object found in the same segment, such as a cluster of tables, will have the same object number In Oracle8, then, a ROWID contains the following information:

•

The data object number

•

The data file (where the first file is 1)

•

The data block within the data file

•

The row in the data block (where the first row is 0)

Usually (and always in Oracle7), a ROWID will uniquely identify a row of data Within Oracle8, however, rows in different tables stored in the same cluster can have the same ROWID value

9.1.3 The DBMS_ROWID Interface

The following sections describe the procedures and functions available through DBMS_ROWID

9.1.3.1 The DBMS_ROWID.ROWID_BLOCK_NUMBER function

The ROWID_BLOCK_NUMBER function returns the block number of a ROWID Its header is,

FUNCTION DBMS_ROWID.ROWID_BLOCK_NUMBER (row_id IN ROWID)

RETURN NUMBER;

where the ROWID parameter is the ROWID from which the value is extracted

9.1.3.1.1 Restrictions

The DBMS_ROWID package supplies the following pragma for ROWID_BLOCK_NUMBER:

PRAGMA RESTRICT_REFERENCES (ROWID_BLOCK_NUMBER, WNDS, RNDS, WNPS, RNPS);

9.1.3.2 The DBMS_ROWID.CREATE_ROWID function

The CREATE_ROWID function creates and returns a ROWID (either restricted or extended, as you request) based on the individual ROWID component values you specify Use this function for test purposes only Here

is its header:

FUNCTION DBMS_ROWID.ROWID_CREATE

(rowid_type IN NUMBER

,object_number IN NUMBER

,relative_fno IN NUMBER

,block_number IN NUMBER

,row_number IN NUMBER)

RETURN ROWID;

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rowid_type The type of ROWID to be created Specify either of the named constants

ROWID_TYPE_RESTRICTED or ROWID_TYPE_EXTENDED

object_number The data object number for the ROWID For a restricted ROWID (Oracle7), use the

ROWID_OBJECT_UNDEFINED constant

relative_fno The relative file number for the ROWID

block_number The block number for the ROWID

row_number The row number for the ROWID

The DBMS_ROWID package supplies the following pragma for CREATE_ROWID:

PRAGMA RESTRICT_REFERENCES (CREATE_ROWID, WNDS, RNDS, WNPS, RNPS);

9.1.3.2.2 Example

Here is an example of a call to the ROWID_CREATE procedure:

my_rowid ROWID;

BEGIN

my_rowid := DBMS_ROWID.ROWID_CREATE

(DBMS_ROWID.ROWID_TYPE_EXTENDED, 100, 15, 103, 345);

END;

/

9.1.3.3 The DBMS_ROWID.ROWID_INFO procedure

The ROWID_INFO procedure parses out and returns the individual components of the specified ROWID Here is its header:

PROCEDURE DBMS_ROWID.ROWID_INFO

(rowid_in IN ROWID

,rowid_type OUT NUMBER

,object_number OUT NUMBER

,relative_fno OUT NUMBER

,block_number OUT NUMBER

,row_number OUT NUMBER);

Parameters are summarized in the following table

Parameter Description

rowid_in The ROWID value to be parsed into components

rowid_type The type of ROWID The value returned will be either of the named constants

ROWID_TYPE_RESTRICTED or ROWID_TYPE_EXTENDED

object_number The data object number for the ROWID For a restricted ROWID (Oracle7), the

ROWID_OBJECT_UNDEFINED constant is returned

relative_fno The relative file number for the ROWID

block_number The block number for the ROWID in the file

row_number The row number for the ROWID

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The DBMS_ROWID package supplies the following pragma for ROWID_INFO:

PRAGMA RESTRICT_REFERENCES (ROWID_INFO, WNDS, RNDS, WNPS, RNPS);

9.1.3.4 The DBMS_ROWID.ROWID_OBJECT function

The ROWID_OBJECT function returns the object number of a ROWID The

ROWID_OBJECT_UNDEFINED constant is returned for restricted ROWIDs Its header is,

FUNCTION DBMS_ROWID.ROWID_OBJECT (row_id IN ROWID)

RETURN NUMBER;

where the row_id parameter is the ROWID from which the value is extracted

The DBMS_ROWID package supplies the following pragma for ROWID_OBJECT:

PRAGMA RESTRICT_REFERENCES (ROWID_OBJECT, WNDS, RNDS, WNPS, RNPS);

9.1.3.4.2 Example

You will want to obtain a ROWID's object number only if the ROWID type is extended You would write code like this to perform that check:

IF DBMS_ROWID.ROWID_TYPE (v_rowid) = DBMS_ROWID.ROWID_TYPE_EXTENDED

THEN

v_objnum := DBMS_ROWID.ROWID_OBJECT (v_rowid);

END IF;

9.1.3.5 The DBMS_ROWID.ROWID_RELATIVE_FNO function

The ROWID_RELATIVE_FNO function returns the relative file number of a ROWID Its header is,

FUNCTION DBMS_ROWID.ROWID_RELATIVE_FNO

(row_id IN ROWID)

RETURN NUMBER;

where the row_id parameter is the ROWID from which the value is extracted

The DBMS_ROWID package supplies the following pragma for ROWID_RELATIVE_FNO:

PRAGMA RESTRICT_REFERENCES (ROWID_RELATIVE_FNO, WNDS, RNDS, WNPS, RNPS);

9.1.3.6 The DBMS_ROWID.ROWID_ROW_NUMBER function

The ROWID_ROW_NUMBER function returns the row number of a ROWID Its header is,

FUNCTION DBMS_ROWID.ROWID_ROW_NUMBER (row_id IN ROWID)

RETURN NUMBER;

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The DBMS_ROWID package supplies the following pragma for ROWID_ROW_NUMBER:

PRAGMA RESTRICT_REFERENCES (ROWID_ROW_NUMBER, WNDS, RNDS, WNPS, RNPS);

9.1.3.7 The DBMS_ROWID.ROWID_TO_ABSOLUTE_FNO function

The ROWID_TO_ABSOLUTE_FNO function returns the absolute file number of a ROWID Here is its header:

FUNCTION DBMS_ROWID.ROWID_TO_ABSOLUTE_FNO

(row_id IN ROWID

,schema_name IN VARCHAR2

,object_name IN VARCHAR2)

RETURN NUMBER;

row_id The ROWID from which the value is extracted

schema_name The name of the schema contains the table

object_name The table name

The DBMS_ROWID package supplies the following pragma for ROWID_RELATIVE_FNO:

PRAGMA RESTRICT_REFERENCES (ROWID_RELATIVE_FNO, WNDS, WNPS, RNPS);

9.1.3.8 The DBMS_ROWID.ROWID_TO_EXTENDED function

The ROWID_TO_EXTENDED function converts a restricted ROWID, addressing a specific row in a table, to

an extended ROWID Here is its header:

FUNCTION DBMS_ROWID.ROWID_TO_EXTENDED

(old_rowid IN ROWID

,schema_name IN VARCHAR2

,object_name IN VARCHAR2

,conversion_type IN INTEGER)

RETURN ROWID;

old_rowid The ROWID to be converted

schema_name The name of the schema that contains the table

object_name The table name

conversion_type The type of conversion Pass either the ROWID_CONVERT_INTERNAL constant (if

old_ROWID was stored in a column of type ROWID) or ROWID_CONVERT_EXTERNAL (if old_ROWID was stored as a character string)

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