122 DBMS_ROWID

Using DBMS_ROWID

• Security Model

• Types

• Exceptions

• Operational Notes

• Examples

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Security Model

This package runs with the privileges of calling user, rather than the package owner SYS.

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Types

• Extension and Restriction Types

• Verification Types

• Object Types

• Conversion Types

Extension and Restriction Types

The types are as follows:

• RESTRICTED—restricted ROWID

• EXTENDED—extended ROWID

For example:

rowid_type_restricted constant integer := 0;
rowid_type_extended   constant integer := 1;

Verification Types

For example:

rowid_is_valid   constant integer := 0;
rowid_is_invalid constant integer := 1;

Object Types

For example:

rowid_object_undefined constant integer := 0;

Conversion Types

For example:

rowid_convert_internal constant integer := 0;
rowid_convert_external constant integer := 1;

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Exceptions

For example:

ROWID_INVALID exception;
   pragma exception_init(ROWID_INVALID, -1410);

ROWID_BAD_BLOCK exception;
   pragma exception_init(ROWID_BAD_BLOCK, -28516);

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Operational Notes

• Some of the functions in this package take a single parameter, such as a ROWID. This can be a character or a PL/SLQ ROWID, either restricted or extended, as required.

• You can call the DBMS_ROWID functions and procedures from PL/SQL code, and you can also use the functions in SQL statements.

  Note:

  ROWID_INFO is a procedure. It can only be used in PL/SQL code.

• You can use functions from the DBMS_ROWID package just like built-in SQL functions; in other words, you can use them wherever you can use an expression. In this example, the ROWID_BLOCK_NUMBER function is used to return just the block number of a single row in the EMP table:

  SELECT DBMS_ROWID.ROWID_BLOCK_NUMBER(rowid)
     FROM emp 
     WHERE ename = 'KING';
  

• If Oracle returns the error "ORA:452, 0, 'Subprogram '%s' violates its associated pragma' for pragma restrict_references, it could mean the violation is due to:

  • A problem with the current procedure or function

  • Calling a procedure or function without a pragma or due to calling one with a less restrictive pragma

  • Calling a package procedure or function that touches the initialization code in a package or that sets the default values

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Examples

This example returns the ROWID for a row in the EMP table, extracts the data object number from the ROWID, using the ROWID_OBJECT function in the DBMS_ROWID package, then displays the object number:

DECLARE
  object_no   INTEGER;
  row_id      ROWID;
  ...
BEGIN
  SELECT ROWID INTO row_id FROM emp
    WHERE empno = 7499;
  object_no := DBMS_ROWID.ROWID_OBJECT(row_id);
  DBMS_OUTPUT.PUT_LINE('The obj. # is '|| object_no);
  ...

Summary of DBMS_ROWID Subprograms

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ROWID_BLOCK_NUMBER Function

This function returns the database block number for the input ROWID.

Syntax

DBMS_ROWID.ROWID_BLOCK_NUMBER (
   row_id      IN   ROWID,
   ts_type_in  IN   VARCHAR2 DEFAULT 'SMALLFILE')
  RETURN NUMBER;

Pragmas

pragma RESTRICT_REFERENCES(rowid_block_number,WNDS,RNDS,WNPS,RNPS);

Parameters

Examples

The example SQL statement selects the block number from a ROWID and inserts it into another table:

INSERT INTO T2 (SELECT dbms_rowid.rowid_block_number(ROWID, 'BIGFILE')
   FROM some_table 
   WHERE key_value = 42);

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ROWID_CREATE Function

This function lets you create a ROWID, given the component parts as parameters.

This is useful for testing ROWID operations, because only the Oracle Server can create a valid ROWID that points to data in a database.

Syntax

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;

Pragmas

pragma RESTRICT_REFERENCES(rowid_create,WNDS,RNDS,WNPS,RNPS);

Parameters

Examples

Create a dummy extended ROWID:

my_rowid := DBMS_ROWID.ROWID_CREATE(1, 9999, 12, 1000, 13);

Find out what the rowid_object function returns:

obj_number := DBMS_ROWID.ROWID_OBJECT(my_rowid);

The variable obj_number now contains 9999.

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ROWID_INFO Procedure

This procedure returns information about a ROWID, including its type (restricted or extended), and the components of the ROWID. This is a procedure, and it cannot be used in a SQL statement.

Syntax

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);

Pragmas

pragma RESTRICT_REFERENCES(rowid_info,WNDS,RNDS,WNPS,RNPS);

Parameters

Examples

This example reads back the values for the ROWID that you created in the ROWID_CREATE:

DBMS_ROWID.ROWID_INFO (
   my_rowid, rid_type, obj_num, file_num, block_num, row_num, 'BIGFILE');

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ROWID_OBJECT Function

This function returns the data object number for an extended ROWID. The function returns zero if the input ROWID is a restricted ROWID.

Syntax

DBMS_ROWID.ROWID_OBJECT (
   rowid_id IN ROWID)
  RETURN NUMBER;

Pragmas

pragma RESTRICT_REFERENCES(rowid_object,WNDS,RNDS,WNPS,RNPS);

Parameters

Examples

SELECT dbms_rowid.rowid_object(ROWID)
   FROM emp
   WHERE empno = 7499;

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ROWID_RELATIVE_FNO Function

This function returns the relative file number of the ROWID specified as the IN parameter. (The file number is relative to the tablespace.)

Syntax

DBMS_ROWID.ROWID_RELATIVE_FNO (
   rowid_id      IN   ROWID,
   ts_type_in    IN   VARCHAR2 DEFAULT 'SMALLFILE')
  RETURN NUMBER;

Pragmas

pragma RESTRICT_REFERENCES(rowid_relative_fno,WNDS,RNDS,WNPS,RNPS);

Parameters

Examples

The example PL/SQL code fragment returns the relative file number:

DECLARE
   file_number    INTEGER;
   rowid_val      ROWID;
BEGIN
   SELECT ROWID INTO rowid_val
     FROM dept 
     WHERE loc = 'Boston';
   file_number :=
     dbms_rowid.rowid_relative_fno(rowid_val, 'SMALLFILE');
    ...

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ROWID_ROW_NUMBER Function

This function extracts the row number from the ROWID IN parameter.

Syntax

DBMS_ROWID.ROWID_ROW_NUMBER (
   row_id IN ROWID)
  RETURN NUMBER;

Pragmas

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

Parameters

Examples

Select a row number:

SELECT dbms_rowid.rowid_row_number(ROWID) 
   FROM emp
   WHERE ename = 'ALLEN';

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ROWID_TO_ABSOLUTE_FNO Function

This function extracts the absolute file number from a ROWID, where the file number is absolute for a row in a given schema and table. The schema name and the name of the schema object (such as a table name) are provided as IN parameters for this function.

Syntax

DBMS_ROWID.ROWID_TO_ABSOLUTE_FNO (
   row_id      IN ROWID,
   schema_name IN VARCHAR2,
   object_name IN VARCHAR2)
  RETURN NUMBER;

Pragmas

pragma RESTRICT_REFERENCES(rowid_to_absolute_fno,WNDS,WNPS,RNPS);

Parameters

Examples

DECLARE
   abs_fno        INTEGER;
   rowid_val      CHAR(18);
   object_name    VARCHAR2(20) := 'EMP';
BEGIN
    SELECT ROWID INTO rowid_val 
     FROM emp
     WHERE empno = 9999;
     abs_fno := dbms_rowid.rowid_to_absolute_fno(
     rowid_val, 'SCOTT', object_name);

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ROWID_TO_EXTENDED Function

This function translates a restricted ROWID that addresses a row in a schema and table that you specify to the extended ROWID format. Later, it may be removed from this package into a different place.

Syntax

DBMS_ROWID.ROWID_TO_EXTENDED (
   old_rowid       IN ROWID,
   schema_name     IN VARCHAR2,   
   object_name     IN VARCHAR2,
   conversion_type IN INTEGER)
  RETURN ROWID;

Pragmas

pragma RESTRICT_REFERENCES(rowid_to_extended,WNDS,WNPS,RNPS);

Parameters

Return Values

ROWID_TO_EXTENDED returns the ROWID in the extended character format. If the input ROWID is NULL, then the function returns NULL. If a zero-valued ROWID is supplied (00000000.0000.0000), then a zero-valued restricted ROWID is returned.

Examples

Assume that there is a table called RIDS in the schema SCOTT, and that the table contains a column ROWID_COL that holds ROWIDs (restricted), and a column TABLE_COL that point to other tables in the SCOTT schema. You can convert the ROWIDs to extended format with the statement:

UPDATE SCOTT.RIDS
   SET rowid_col =
   dbms_rowid.rowid_to_extended (
      rowid_col, 'SCOTT", TABLE_COL, 0);

Usage Notes

If the schema and object names are provided as IN parameters, then this function verifies SELECT authority on the table named, and converts the restricted ROWID provided to an extended ROWID, using the data object number of the table. That ROWID_TO_EXTENDED returns a value, however, does not guarantee that the converted ROWID actually references a valid row in the table, either at the time that the function is called, or when the extended ROWID is actually used.

If the schema and object name are not provided (are passed as NULL), then this function attempts to fetch the page specified by the restricted ROWID provided. It treats the file number stored in this ROWID as the absolute file number. This can cause problems if the file has been dropped, and its number has been reused prior to the migration. If the fetched page belongs to a valid table, then the data object number of this table is used in converting to an extended ROWID value. This is very inefficient, and Oracle recommends doing this only as a last resort, when the target table is not known. The user must still know the correct table name at the time of using the converted value.

If an extended ROWID value is supplied, the data object number in the input extended ROWID is verified against the data object number computed from the table name parameter. If the two numbers do not match, the INVALID_ROWID exception is raised. If they do match, the input ROWID is returned.

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ROWID_TO_RESTRICTED Function

This function converts an extended ROWID into restricted ROWID format.

Syntax

DBMS_ROWID.ROWID_TO_RESTRICTED (
   old_rowid       IN ROWID,
   conversion_type IN INTEGER)
  RETURN ROWID;

Pragmas

pragma RESTRICT_REFERENCES(rowid_to_restricted,WNDS,RNDS,WNPS,RNPS);

Parameters

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ROWID_TYPE Function

This function returns 0 if the ROWID is a restricted ROWID, and 1 if it is extended.

Syntax

DBMS_ROWID.ROWID_TYPE (
   rowid_id IN ROWID)
  RETURN NUMBER;

Pragmas

pragma RESTRICT_REFERENCES(rowid_type,WNDS,RNDS,WNPS,RNPS);

Parameters

Examples

IF DBMS_ROWID.ROWID_TYPE(my_rowid) = 1 THEN
   my_obj_num := DBMS_ROWID.ROWID_OBJECT(my_rowid);

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ROWID_VERIFY Function

This function verifies the ROWID. It returns 0 if the input restricted ROWID can be converted to extended format, given the input schema name and table name, and it returns 1 if the conversion is not possible.

Syntax

DBMS_ROWID.ROWID_VERIFY (
   rowid_in        IN ROWID,
   schema_name     IN VARCHAR2,
   object_name     IN VARCHAR2,
   conversion_type IN INTEGER
  RETURN NUMBER;

Pragmas

pragma RESTRICT_REFERENCES(rowid_verify,WNDS,WNPS,RNPS);

Parameters

Examples

Considering the schema in the example for the ROWID_TO_EXTENDED function, you can use the following statement to find bad ROWIDs prior to conversion. This enables you to fix them beforehand.

SELECT ROWID, rowid_col 
   FROM SCOTT.RIDS
   WHERE dbms_rowid.rowid_verify(rowid_col, NULL, NULL, 0) =1;