3 Workspace Manager Valid Time Support

This chapter describes the support for valid time, also known as effective dating, with version-enabled tables. It contains the following major sections:

Section 3.1, "Valid Time Support: Introduction and Example"
Section 3.2, "WM_PERIOD Data Type"
Section 3.3, "Valid Time Constants"
Section 3.4, "API Features for Valid Time Support"
Section 3.5, "Operators for Valid Time Support"
Section 3.6, "Queries and DML Operations with Valid Time Support"
Section 3.7, "Constraint Management for Valid Time Support"
Section 3.8, "Locking with Valid Time Support"
Section 3.9, "Metadata Views Affected by Valid Time Support"
Section 3.10, "SQL* Loader Support for Valid Times"
Section 3.11, "Adding Valid Time Support to an Existing Table"

3.1 Valid Time Support: Introduction and Example

Some applications need to store data with an associated time range that indicates the validity of the data. That is, each record is valid only within the time range associated with the record.

Workspace Manager lets you enable valid time support when you version-enable a table. (You can also add valid time support to an existing version-enabled table, as explained in Section 3.11.) If you enable valid time support, each row contains an added column to hold the valid time period associated with the row. You can specify a valid time range for the session, and Workspace Manager will ensure that queries and insert, update, and delete operations correctly reflect and accommodate the valid time range. The valid time range specified can be in the past or the future, or it can include the past, present, and future.

Example 3-1 presents a simple example of valid time support. The example does the following:

Creates a table of employees and their salaries.
Version-enables the table, specifying valid time support, which causes a column named WM_VALID to be added to the table automatically.
Inserts rows into the table. For each row, it specifies the employee name, salary, and valid time period.
Sets the valid time range for the session.
Updates a row, specifying a new salary and valid time period for an employee.
Disables versioning on the table.

Example 3-1:

Refers to valid time support concepts and techniques that will be explained in other sections of this chapter.
Assumes that you are familiar with the Workspace Manager concepts and techniques explained in Chapter 1.
Does not create workspaces or savepoints. (These are shown in Example 1-3 and Example 1-4 in Section 1.17.)

Example 3-1 Valid Time Support

-- Create a very simple employees table (deliberately oversimplified
-- for purposes of illustration).
CREATE TABLE employees (
  name VARCHAR2(16) PRIMARY KEY,
  salary NUMBER 
);

-- Version-enable the table. Specify TRUE for valid time support.
EXECUTE DBMS_WM.EnableVersioning ('employees', 'VIEW_WO_OVERWRITE', FALSE, TRUE);

INSERT INTO employees VALUES(
  'Adams',
  30000,
  WMSYS.WM_PERIOD(TO_DATE('01-01-1990', 'MM-DD-YYYY'), 
                  TO_DATE('01-01-2005', 'MM-DD-YYYY'))
);
INSERT INTO employees VALUES(
  'Baxter',
  40000,
  WMSYS.WM_PERIOD(TO_DATE('01-01-2000', 'MM-DD-YYYY'), DBMS_WM.UNTIL_CHANGED)
);

INSERT INTO employees VALUES(
  'Coleman',
  50000,
  WMSYS.WM_PERIOD(TO_DATE('01-01-2003', 'MM-DD-YYYY'), 
                  TO_DATE('12-31-9999', 'MM-DD-YYYY'))
);

COMMIT;

-- Set valid time period to virtually all time.
EXECUTE DBMS_WM.SetValidTime(TO_DATE('01-01-1900', 'MM-DD-YYYY'),
  TO_DATE('01-01-9999', 'MM-DD-YYYY'));

-- Update the salary for an existing employee. Perform "sequenced" update, so
-- that existing time-related information is preserved. This results in two rows
-- for Baxter.
-- First, set valid time to the intended range for Baxter's raise.
EXECUTE DBMS_WM.SetValidTime(TO_DATE('01-01-2003', 'MM-DD-YYYY'), DBMS_WM.UNTIL_CHANGED);
-- Give Baxter a raise, effective 01-Jan-2003 until changed.
UPDATE employees SET salary = 45000 WHERE name = 'Baxter';

-- Disable versioning. By default (keepWMValid parameter value of TRUE),
-- the WM_VALID column is kept, with all its data. 
COMMIT;
EXECUTE DBMS_WM.DisableVersioning ('employees');

3.2 WM_PERIOD Data Type

The WM_PERIOD data type is used to specify a valid time range for the session or workspace, and for a row in a version-enabled table. The WM_PERIOD type is defined as follows:

CREATE TYPE WM_PERIOD AS OBJECT  (
  validFrom  TIMESTAMP WITH TIME ZONE,
  validTill      TIMESTAMP WITH TIME ZONE );

The validFrom date is inclusive, and the validTill period is exclusive; that is, the valid date range starts on the validFrom date and extends up to but not including the validTill date.

Example 3-2 sets the session valid time range to 01-Jan-2003.

Example 3-2 Setting the Session Valid Time to a Specific Date

EXECUTE DBMS_WM.SetValidTime(TO_DATE('01-01-2003', 'MM-DD-YYYY'), TO_DATE('01-02-2003', 'MM-DD-YYYY'));

Example 3-3 inserts a row that is valid from 01-Jan-2003 until it is changed.

Example 3-3 Inserting a Row Valid for a Time Range

INSERT INTO employees VALUES(
  'Baxter',
  40000,
  WMSYS.WM_PERIOD(TO_DATE('01-01-2003', 'MM-DD-YYYY'), DBMS_WM.UNTIL_CHANGED)
);

3.3 Valid Time Constants

Table 3-1 lists constants that can be used in the validFrom and validTill timestamps of a WM_PERIOD specification.

Table 3-1 Constants for Valid Time Support

Constant	Explanation
DBMS_WM.MIN_TIME	The minimum (earliest) timestamp value supported by Workspace Manager. Currently the beginning of the day on 01-Jan in the year -4713 (4713 BCE).
DBMS_WM.MAX_TIME	The maximum (latest) timestamp value supported by Workspace Manager. Currently the end of the day on 31-Dec-9999.
DBMS_WM.UNTIL_CHANGED	A timestamp that is treated as DBMS_WM.MAX_TIME until a subsequent modification overrides the value.

3.4 API Features for Valid Time Support

Table 3-2 lists DBMS_WM subprograms that are devoted to valid time support or that have parameters related to valid time support.

Table 3-2 API Features for Valid Time Support

Subprogram	Valid Time Support
EnableVersioning	If the `validTime` parameter value is TRUE, the table is version-enabled `with` valid time support. A column named `WM_VALID` of type WM_PERIOD is added to the table. For any existing rows, the `WM_VALID` column is set with a `validFrom` timestamp of SYSTIMESTAMP and a `validTill` timestamp of DBMS_WM.UNTIL_CHANGED.
DisableVersioning	The `keepWMValid` parameter determines whether to keep (the default) or delete the `WM_VALID` column and its data when the table is version-disabled.
GetValidFrom	Returns the `validFrom` timestamp from the session valid time period.
GetValidTill	Returns the `validTill` timestamp from the session valid time period.
SetValidTime	Sets the session valid time period to the specified range. You can execute the procedure with no parameters (to have the valid time range set as from the current time and until changed), with only the `validFrom` parameter, or with both the `validFrom` and `validTill` parameters.
SetWMValidTimeFilterOFF	Removes the valid time filter for the current session.
SetWMValidTimeFilterON	Sets a valid time filter for the current session (that is, a time to be applied to version-enabled tables.
SetWMValidUpdateModeOFF	Disables sequenced and nonsequenced update operations and sequenced delete operations on tables that have valid time support.
SetWMValidUpdateModeON	Enables sequenced and nonsequenced update operations and sequenced delete operations on tables that have valid time support.

3.5 Operators for Valid Time Support

Workspace Manager provides relationship checking operators and set operators that accept two time period parameters and that can be used to apply valid time filters in a query.

The relationship checking operators return the integer value 1 if the relationship between the two periods exists, and 0 if the relationship does not exist. The following relationship checking operators for are provided for valid time support:

WM_OVERLAPS checks if two periods overlap.
WM_CONTAINS checks if the first period contains the second period.
WM_MEETS checks if the end of the first period is the start of the second period.
WM_EQUALS checks if the two periods are equal (that is, their start and end times are the same).
WM_LESSTHAN checks if the end of the first period is less than (that is, earlier than) the start of the second period.
WM_GREATERTHAN checks if the start of the first period is greater than (that is, later than) the end of the second period.

The set operators return the period reflecting the relationship between the two periods, or a null value if the two periods do not have the specified relationship. The following set operators for are provided for valid time support:

WM_INTERSECTION returns the intersection of the two periods, that is, the time range common to both periods.
WM_LDIFF returns the difference between the two periods on the left (that is, earlier in time).
WM_RDIFF returns the difference between the two periods on the right (that is, later in time).

You can use the relationship checking operators as alternatives to using the wm_valid.validFrom and wm_valid.validTill attributes of the row. For example, the following two queries, which select data valid on 01-Jan-1991, are equivalent:

SELECT * FROM employees e WHERE WM_CONTAINS (e.wm_valid,
   WMSYS.WM_PERIOD(TO_DATE('01-01-1991', 'MM-DD-YYYY'), 
                   TO_DATE('01-02-1991', 'MM-DD-YYYY')) = 1;
SELECT * from employees e 
   WHERE e.wm_valid.validFrom <= TO_DATE('01-01-1991', 'MM-DD-YYYY')
     AND e.wm_valid.validTill > TO_DATE('01-03-1991', 'MM-DD-YYYY');

The rest of this section contains additional information about each operator. The operators are listed in alphabetical order.

3.5.1 WM_CONTAINS

The WM_CONTAINS operator checks if the first period contains the second period. WM_CONTAINS(p1, p2) returns 1 only if the period p1 contains the period p2; otherwise, it returns 0.

For example:

WM_CONTAINS(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1985', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1988', 'MM-DD-YYYY') = 1

WM_CONTAINS(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1985', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1995', 'MM-DD-YYYY') = 0

Example 3-4 returns all rows in the EMPLOYEES table that were valid on 01-Jan-1995 (that is, where the WM_VALID column value contains the period for 01-Jan-1995).

Example 3-4 WM_CONTAINS Operator

SELECT * FROM employees e
  WHERE WM_CONTAINS(e.wm_valid,
    wm_period(TO_DATE('01-01-1995', 'MM-DD-YYYY'),
              TO_DATE('01-02-1995', 'MM-DD-YYYY'))) = 1;

NAME                 SALARY                                                     
---------------- ----------                                                     
WM_VALID(VALIDFROM, VALIDTILL)                                                  
--------------------------------------------------------------------------------
Adams                 30000                                                     
WM_PERIOD('01-JAN-1990 12:00:00 -04:00', '01-JAN-2005 12:00:00 -04:00')

3.5.2 WM_EQUALS

The WM_EQUALS operator checks if the first period is equal to (that is, the same as) the second period. WM_CONTAINS(p1, p2) returns 1 only if the period p1 is equal to the period p2; otherwise, it returns 0.

For example:

WM_EQUALS(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY') = 1

WM_EQUALS(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1985', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1995', 'MM-DD-YYYY') = 0

Example 3-5 returns all rows in the EMPLOYEES table that are valid from 01-Jan-1990 until 01-Jan-2005 (that is, where the WM_VALID column value is equal to that period).

Example 3-5 WM_EQUALS Operator

SELECT * FROM employees e
  WHERE WM_EQUALS(e.wm_valid,
    wm_period(TO_DATE('01-01-1990', 'MM-DD-YYYY'),
              TO_DATE('01-01-2005', 'MM-DD-YYYY'))) = 1;

NAME                 SALARY                                                     
---------------- ----------                                                     
WM_VALID(VALIDFROM, VALIDTILL)                                                  
--------------------------------------------------------------------------------
Adams                 30000                                                     
WM_PERIOD('01-JAN-1990 12:00:00 -04:00', '01-JAN-2005 12:00:00 -04:00')

3.5.3 WM_GREATERTHAN

The WM_GREATERTHAN operator checks if the first period is greater than (that is, occurs after) the second period. WM_CONTAINS(p1, p2) returns 1 only if the entire period p1 is later than the period p2; otherwise, it returns 0.

For example:

WM_GREATERTHAN(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1970', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1980', 'MM-DD-YYYY') = 1

WM_GREATERTHAN(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1970', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1981', 'MM-DD-YYYY') = 0

Example 3-6 returns all rows in the EMPLOYEES table that are valid only after 01-Jan-2001 (that is, where the WM_VALID column timestamps are both after 01-Jan-2001).

Example 3-6 WM_GREATERTHAN Operator

SELECT * FROM employees e
  WHERE WM_GREATERTHAN(e.wm_valid,
    wm_period(TO_DATE('01-01-2001', 'MM-DD-YYYY'),
              TO_DATE('01-02-2001', 'MM-DD-YYYY'))) = 1;

NAME                 SALARY                                                     
---------------- ----------                                                     
WM_VALID(VALIDFROM, VALIDTILL)                                                  
--------------------------------------------------------------------------------
Coleman               50000                                                     
WM_PERIOD('01-JAN-2003 12:00:00 -04:00', '31-DEC-9999 12:00:00 -04:00')

3.5.4 WM_INTERSECTION

The WM_INTERSECTION operator returns the intersection of the two periods, that is, the period common to both specified periods. WM_INTERSECTION(p1, p2) returns a period that is the intersection of periods p1 and p2.

The following example returns the period between 01-Jan-1985 to 01-Jan-1988:

WM_INTERSECTION(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
                   TO_DATE('01-01-1990', 'MM-DD-YYYY')
                TO_DATE('01-01-1985', 'MM-DD-YYYY'), 
                   TO_DATE('01-01-1988', 'MM-DD-YYYY')

The following example returns the period between 01-Jan-1985 to 01-Jan-1990:

WM_INTERSECTION(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
                   TO_DATE('01-01-1990', 'MM-DD-YYYY')
                TO_DATE('01-01-1985', 'MM-DD-YYYY'), 
                   TO_DATE('01-01-1995', 'MM-DD-YYYY')

The following example returns a null value, because there is no intersection of the periods:

WM_INTERSECTION(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
                   TO_DATE('01-01-1990', 'MM-DD-YYYY')
                TO_DATE('01-01-1992', 'MM-DD-YYYY'), 
                   TO_DATE('01-01-1995', 'MM-DD-YYYY')

Example 3-7 returns, for each row in the EMPLOYEES table, the employee name and the period in which the WM_PERIOD column value intersects the period on 01-Jan-1995.

Example 3-7 WM_INTERSECTION Operator

SELECT e.name, WM_INTERSECTION(e.wm_valid,
  wm_period(TO_DATE('01-01-1995', 'MM-DD-YYYY'),
            TO_DATE('01-02-1995', 'MM-DD-YYYY')))
 FROM employees e;

NAME                                                                            
----------------                                                                
WM_INTERSECTION(E.WM_VALID,WM_PERIOD(TO_DATE('01-01-1995','MM-DD-
--------------------------------------------------------------------------------
Adams                                                                           
WM_PERIOD('01-JAN-1995 12:00:00 -04:00', '02-JAN-1995 12:00:00 -04:00')         
                                                                                
Baxter                                                                          
                                                                                
                                                                                
Coleman

As you can see in the output of Example 3-7, only Adams has a row that is valid on 01-Jan-1995.

3.5.5 WM_LDIFF

The WM_LDIFF operator returns the difference between the two periods on the left (that is, earlier in time). WM_LDIFF(p1, p2) returns a period that is the difference between periods p1 and p2 on the left.

The following example returns the period between 01-Jan-1980 to 01-Jan-1985:

WM_LDIFF(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
                     TO_DATE('01-01-1990', 'MM-DD-YYYY')
                  TO_DATE('01-01-1985', 'MM-DD-YYYY'), 
                     TO_DATE('01-01-1988', 'MM-DD-YYYY')

The following example returns a null value because p1.validFrom is greater than p2.validFrom:

WM_LDIFF(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
                     TO_DATE('01-01-1990', 'MM-DD-YYYY')
                  TO_DATE('01-01-1975', 'MM-DD-YYYY'), 
                     TO_DATE('01-01-1995', 'MM-DD-YYYY')

The following example returns a null value because p2 is completely outside (in this case, later than) p1:

WM_LDIFF(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
                     TO_DATE('01-01-1990', 'MM-DD-YYYY')
                  TO_DATE('01-01-1992', 'MM-DD-YYYY'), 
                     TO_DATE('01-01-1995', 'MM-DD-YYYY')

Example 3-8 returns, for each row in the EMPLOYEES table, the employee name and the period in which the WM_PERIOD column value is different on the left from 01-Jan-1995.

Example 3-8 WM_LDIFF Operator

SELECT e.name, WM_LDIFF(e.wm_valid,
  wm_period(TO_DATE('01-01-1995', 'MM-DD-YYYY'),
            TO_DATE('01-02-1995', 'MM-DD-YYYY')))
 FROM employees e;

NAME                                                                            
----------------                                                                
WM_LDIFF(E.WM_VALID,WM_PERIOD(TO_DATE('01-01-1995','MM-DD-YYYY'),
--------------------------------------------------------------------------------
Adams                                                                           
WM_PERIOD('01-JAN-1990 12:00:00 -04:00', '01-JAN-1995 12:00:00 -04:00')         
                                                                                
Baxter                                                                          
                                                                                
                                                                                
Coleman

As you can see in the output of Example 3-8, only Adams has a row that is valid during the period of difference on the left.

3.5.6 WM_LESSTHAN

The WM_LESSTHAN operator checks if the first period is less than (that is, occurs before) the second period. WM_CONTAINS(p1, p2) returns 1 only if the entire period p1 is less than the period p2; otherwise, it returns 0.

For example:

WM_LESSTHAN(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1991', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1992', 'MM-DD-YYYY') = 1

WM_LESSTHAN(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1989', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1992', 'MM-DD-YYYY') = 0

Example 3-9 returns all rows in the EMPLOYEES table that are valid only before 01-Jan-2010 (that is, where the WM_VALID column timestamps are both before 01-Jan-2001).

Example 3-9 WM_LESSTHAN Operator

SELECT * FROM employees e
  WHERE WM_LESSTHAN(e.wm_valid,
    wm_period(TO_DATE('01-01-2010', 'MM-DD-YYYY'),
              TO_DATE('01-02-2010', 'MM-DD-YYYY'))) = 1;

NAME                 SALARY                                                     
---------------- ----------                                                     
WM_VALID(VALIDFROM, VALIDTILL)                                                  
--------------------------------------------------------------------------------
Adams                 30000                                                     
WM_PERIOD('01-JAN-1990 12:00:00 -04:00', '01-JAN-2005 12:00:00 -04:00')

3.5.7 WM_MEETS

The WM_MEETS operator checks if the end of the first period is the start of the second period. WM_MEETS(p1, p2) returns 1 only if p1.validTill = p2.validFrom; otherwise, it returns 0.

For example:

WM_MEETS(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1990', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1988', 'MM-DD-YYYY') = 1

WM_MEEETS(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1992', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1995', 'MM-DD-YYYY') = 0

Example 3-10 returns all rows in the EMPLOYEES table that are valid only if the ending timestamp of the valid date period is the same as the start of the period from 01-Jan-2005 until 01-Jan-2006 (that is, if WM_VALID.validTill is equal to the start of the specified period).

Example 3-10 WM_MEETS Operator

SELECT * FROM employees e
  WHERE WM_MEETS(e.wm_valid,
    wm_period(TO_DATE('01-01-2005', 'MM-DD-YYYY'),
              TO_DATE('01-01-2006', 'MM-DD-YYYY'))) = 1;

NAME                 SALARY                                                     
---------------- ----------                                                     
WM_VALID(VALIDFROM, VALIDTILL)                                                  
--------------------------------------------------------------------------------
Adams                 30000                                                     
WM_PERIOD('01-JAN-1990 12:00:00 -04:00', '01-JAN-2005 12:00:00 -04:00')

3.5.8 WM_OVERLAPS

The WM_OVERLAPS operator checks if two periods overlap. WM_OVERLAPS(p1, p2) returns 1 if the periods p1 and p2 overlap; otherwise, it returns 0.

For example:

WM_OVERLAPS(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1985', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1995', 'MM-DD-YYYY') = 1

WM_OVERLAPS(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1990', 'MM-DD-YYYY')
            TO_DATE('01-01-1970', 'MM-DD-YYYY'), 
               TO_DATE('01-01-1980', 'MM-DD-YYYY') = 0

Example 3-11 returns all rows in the EMPLOYEES table whose valid date range overlaps the period from 01-Jan-1990 until 01-Jan-2000.

Example 3-11 WM_OVERLAPS Operator

SELECT * FROM employees e
  WHERE WM_OVERLAPS(e.wm_valid,
    wm_period(TO_DATE('01-01-1990', 'MM-DD-YYYY'),
              TO_DATE('01-01-2000', 'MM-DD-YYYY'))) = 1;

NAME                 SALARY                                                     
---------------- ----------                                                     
WM_VALID(VALIDFROM, VALIDTILL)                                                  
--------------------------------------------------------------------------------
Adams                 30000                                                     
WM_PERIOD('01-JAN-1990 12:00:00 -04:00', '01-JAN-2005 12:00:00 -04:00')

3.5.9 WM_RDIFF

The WM_RDIFF operator returns the difference between the two periods on the right (that is, later in time). WM_RDIFF(p1, p2) returns a period that is the difference between periods p1 and p2 on the right.

The following example returns the period between 01-Jan-1988 to 01-Jan-1990:

WM_RDIFF(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
                      TO_DATE('01-01-1990', 'MM-DD-YYYY')
                   TO_DATE('01-01-1985', 'MM-DD-YYYY'), 
                      TO_DATE('01-01-1988', 'MM-DD-YYYY')

The following example returns a null value because p1.validTill is less than p2.validTill:

WM_RDIFF(TO_DATE('01-01-1980', 'MM-DD-YYYY'), 
                      TO_DATE('01-01-1990', 'MM-DD-YYYY')
                   TO_DATE('01-01-1975', 'MM-DD-YYYY'), 
                      TO_DATE('01-01-1995', 'MM-DD-YYYY')

Example 3-12 returns, for each row in the EMPLOYEES table, the employee name and the period in which the WM_PERIOD column value is different on the right from 01-Jan-1995.

Example 3-12 WM_RDIFF Operator

SELECT e.name, WM_RDIFF(e.wm_valid,
  wm_period(TO_DATE('01-01-1995', 'MM-DD-YYYY'),
            TO_DATE('01-02-1995', 'MM-DD-YYYY')))
 FROM employees e;

NAME                                                                            
----------------                                                                
WM_RDIFF(E.WM_VALID,WM_PERIOD(TO_DATE('01-01-1995','MM-DD-YYYY'),
--------------------------------------------------------------------------------
Adams                                                                           
WM_PERIOD('02-JAN-1995 12:00:00 -04:00', '01-JAN-2005 12:00:00 -04:00')         
                                                                                
Baxter                                                                          
                                                                                
                                                                                
Coleman                                                                         
WM_PERIOD('01-JAN-2003 12:00:00 -04:00', '31-DEC-9999 12:00:00 -04:00')

As you can see in the output of Example 3-12, only Adams and Coleman have rows that are valid during the period of difference on the right.

3.6 Queries and DML Operations with Valid Time Support

This section describes some behaviors and considerations for queries and data manipulation language (insert, update, and delete) operations related to valid time support.

3.6.1 Queries

All queries issued against a version-enabled table with valid time support take into account the current session's valid time setting (set using the SetValidTime or SetWMValidTimeFilterON procedure). Unless the query specifies otherwise (for example, by using one of the valid time support operators described in Section 3.5), each query displays all rows from the underlying table having a valid time range that overlaps the session valid time or valid time filter, and that satisfy the other conditions of the query.

By default (that is, if the SetValidTime procedure has not been invoked in the session or if it was invoked with no parameters), all rows that are valid at the current time are considered valid, and the valid time period is considered to be from the current time forward without limit.

3.6.2 Data Manipulation (DML) Operations

All DML statements (INSERT, UPDATE, and DELETE) issued against a version-enabled table with valid time support take into account the current session's valid time setting and update mode. (The update mode is controlled by the SetWMValidUpdateModeON and SetWMValidUpdateModeOFF procedures.) The DML statements can affect all rows that are valid for the valid time period.

By default (that is, if the SetValidTime procedure has not been invoked in the session or if it was invoked with no parameters), all rows that are valid at the current time can be affected by DML statements, and all modified rows have their valid time range timestamps set as from the current time until changed.

The following sections describe additional considerations that apply to specific kinds of DML operations.

3.6.2.1 Update Operations

Update operations to version-enabled tables with valid time support can be sequenced or nonsequenced.

A sequenced update operation occurs when you do not specify a change to the WM_VALID column in the UPDATE statement. In a sequenced update operation, the WM_VALID.ValidTill value for the row is changed to the ValidFrom timestamp of the current session valid time range, and a new row is created in which the WM_VALID period reflects the current session valid time range. Sequenced updates ensure that no duplicate records are created by an UPDATE statement, because the WM_VALID column values are different.

Example 3-13 shows a sequenced update operation, in which employee Baxter is given a raise. Before the update, there is one row for Baxter, with a salary of 40000 and a valid time period from 01-Jan-2000 until changed.

Example 3-13 Sequenced Update Operation

-- Update the salary for an existing employee. Perform "sequenced" update, so
-- that existing time-related information is preserved. This results in two rows
-- for Baxter.
-- First, set valid time to the intended range for Baxter's raise.
EXECUTE DBMS_WM.SetValidTime(TO_DATE('01-01-2003', 'MM-DD-YYYY'), 
  DBMS_WM.UNTIL_CHANGED);
-- Give Baxter a raise, effective 01-Jan-2003 until changed.
UPDATE employees SET salary = 45000 WHERE name = 'Baxter';

The update operation in Example 3-13 modifies the WM_VALID value of the existing row and creates a new row with the new salary value and the WM_VALID value reflecting the session valid time range, as shown by the following statements:

-- Set valid time to encompass virtually all time.
EXECUTE DBMS_WM.SetValidTime(TO_DATE('01-01-1900', 'MM-DD-YYYY'), TO_DATE('01-02-9999', 'MM-DD-YYYY'));

-- See what data exists for Baxter.
SELECT * FROM employees WHERE name = 'Baxter';

NAME                 SALARY
---------------- ----------
WM_VALID(VALIDFROM, VALIDTILL)
--------------------------------------------------------------------------------
Baxter                45000
WM_PERIOD('01-JAN-2003 12:00:00 -04:00', NULL)

Baxter                40000
WM_PERIOD('01-JAN-2000 12:00:00 -04:00', '01-JAN-2003 12:00:00 -04:00')

A sequenced delete operation deletes the portion of a row that falls within the session valid time range; that is, a new row is created in which the WM_VALID period reflects the current session valid time range, and then that row is deleted. If the UPDATE statement in Example 3-13 had instead been DELETE FROM employees WHERE name = 'Baxter';, the new row for Baxter, valid from 01-Jan-2003 until changed, would have been deleted, but any rows for Baxter valid before 01-Jan-2003 would not be affected. There is no concept of a non-sequenced delete operation; for example, if a valid time was not set in Example 3-13, a delete operation WHERE name = 'Baxter' would delete all rows for Baxter.

Sequenced update and delete operations are enabled when a table is version-enabled with valid time support or when valid time support is added to a version-enabled table. However, you can disable support for sequenced update and delete operations (as well as for nonsequenced update operations) by using the SetWMValidUpdateModeOFF procedure, and you can re-enable support by using the SetWMValidUpdateModeON procedure. (Both procedures are described in Chapter 4.)

A nonsequenced update operation occurs when you specify a change to the WM_VALID column in the UPDATE statement. In a nonsequenced update operation, no additional row is created, and the WM_VALID column value of the updated row or rows reflects what you specified in the UPDATE statement. You must ensure that a nonsequenced update operation will not result in multiple rows with the same primary key value being valid in the period specified in the UPDATE statement; otherwise, the update fails because of a primary key constraint violation.

If the UPDATE statement in Example 3-13 had been a nonsequenced update operation, the result would have been only one row for Baxter: the existing row would have had the salary set to 45000 and the WM_VALID column set to the period specified in the UPDATE statement.

3.6.2.2 Insert Operations

When you insert a row into a version-enabled table with valid time support, you can specify a valid time period for the row. If you specify null timestamps for the period, the session valid time period is used.

When a row is inserted into a version-enabled table with valid time support, Workspace Manager checks to ensure that no existing rows with the same primary key value have a valid time range that overlaps the valid time range of the newly inserted row. If such a row is found, an exception is raised. Example 3-14 shows an attempted insert operation that violates a primary key constraint because overlapping valid time periods.

Example 3-14 Insert Operation Failing Because of Overlapping Time Periods

-- Insert. Should violate primary key constraint, because of overlapping times:
-- existing Coleman row is valid from 01-Jan-2003 until 31-Dec-9999.
INSERT INTO employees VALUES(
  'Coleman',
  55000,
  WMSYS.WM_PERIOD(TO_DATE('01-01-2004', 'MM-DD-YYYY'),
                  TO_DATE('12-31-9999', 'MM-DD-YYYY'))
);
)
*
ERROR at line 6:
ORA-20010: unique key violation 
ORA-06512: at "WM_DEVELOPER.OVM_INSERT_10", line 1 
ORA-04088: error during execution of trigger 'WM_DEVELOPER.OVM_INSERT_10'

To make the statement in Example 3-14 succeed, first change the WM_VALID.ValidTill attribute for the Coleman row to a timestamp reflecting 01-Jan-2004 or an earlier date.

3.7 Constraint Management for Valid Time Support

This section describes considerations related to valid time support that affect referential integrity constraints and unique constraints.

3.7.1 Referential Integrity Constraints

If a referential integrity constraint exists between two version-enabled tables that have valid time support, the valid time periods of rows are considered when the constraint is enforced. For example, assume that a DEPARTMENTS table has a MANAGER_ID column that is a foreign key referencing the EMPLOYEE_ID column in an EMPLOYEES table (that is, the department manager must be an existing employee). If both tables are version-enabled with valid time support, and if an insert or update operation would result in a new DEPARTMENTS.MANAGER_ID value, the operation will fail if the DEPARTMENTS.WM_VALID value is not within the range of the EMPLOYEES.WM_VALID value for the employee who is being made the department manager. (That is, the operation will fail if the new department manager is not a valid employee for the time period specified or defaulted for the insert or update operation.)

If either or both tables in a referential integrity constraint are not version-enabled with valid time support, valid time periods are ignored in enforcing the constraint.

3.7.2 Unique Constraints

If a unique constraint exists in a version-enabled table with valid time support, the valid time periods of rows are considered when the constraint is enforced. For example, assume that an EMPLOYEES table has an EMPLOYEE_ID column that has a unique constraint. If an insert or update operation would result in a new EMPLOYEE_ID value that is the same as an existing EMPLOYEE_ID value, the operation will fail if the WM_VALID values of the existing and inserted rows overlap. (That is, the operation will fail if the new employee and an existing employee have the same ID numbers and their rows are both valid at any given time. However, the operation will succeed if the valid time periods for the two employees do not overlap.)

3.8 Locking with Valid Time Support

If a row in a version-enabled table with valid time support is locked, it is automatically locked for its entire valid time period. There is no way to lock a row for a specified time period.

Any updates in a pessimistically locked workspace will lock the rows seen from an ancestor workspace as the updates are performed in the workspace. The locked rows in ancestor workspaces will not be further updatable in their valid time periods as long as they are locked.

For an explanation of Workspace Manager locking, see Section 1.3.

3.9 Metadata Views Affected by Valid Time Support

This section describes the effect on valid time support on Workspace Manager metadata views. These views are documented in Chapter 5.

3.9.1 xxx_CONF Views and Valid Time Support

For a versioned-enabled table with valid time support, the xxx_CONF view (described in Section 5.42) will include any temporal conflicts. Such a conflict results when the valid time of a row in a parent workspace, containing the same key as a row in its child workspace, overlaps with the valid time of that row in the child workspace. Setting the session context valid time has no effect on the results of the xxx_CONF views, because all applicable conflicts are displayed for the entire time dimension.

For a version-enabled table with valid time support, a column named WM_VALID, of type WM_PERIOD, is added to the xxx_CONF view, to indicate the time period during which the row is valid. A column named WM_CONFLICTPERIOD, of type WM_PERIOD, is also added to the view, to indicate the overlapping period of the rows for which conflicts were detected.

3.9.2 xxx_DIFF Views and Valid Time Support

For a version-enabled table with valid time support, the xxx_DIFF view (described in Section 5.43) will include temporal differences for a primary key between two distinct workspaces or savepoints. Such a difference occurs when a row is modified (inserted, updated, or deleted) in either a parent or child workspace. If two rows with the same primary key value are modified in both a parent and child workspace, the two rows are only correlated in the xxx_DIFF view when the valid time ranges of the rows overlap. Setting the session context valid time has no effect on the results of the xxx_DIFF views, because all applicable differences are displayed for the entire time dimension.

For a version-enabled table with valid time support, a column named WM_VALID, of type WM_PERIOD, is added to the xxx_DIFF view, to indicate the time period during which the row is valid. A column named WM_DIFFPERIOD, of type WM_PERIOD, is also added to the view, to indicate the overlapping period of the rows for which a difference was detected.

3.9.3 xxx_HIST Views and Valid Time Support

The xxx_HIST views (described in Section 5.44) include information about both valid times and transaction times. It also includes audit information, such as the name of the user that created the row. For a version-enabled table with valid time support, a column named WM_VALID, of type WM_PERIOD, is added to the xxx_HIST view, to indicate the time period during which the row is valid.

3.9.4 xxx_LOCK Views and Valid Time Support

For a version-enabled table with valid time support, a column named WM_VALID, of type WM_PERIOD, is added to the xxx_LOCK view (described in Section 5.45), to indicate the time period during which the row is valid. The row is locked for its entire valid time period, so this is also the locking period.

3.9.5 xxx_MW Views and Valid Time Support

For a version-enabled table with valid time support, a column named WM_VALID, of type WM_PERIOD, is added to the xxx_MW view (described in Section 5.46), to indicate the time period during which the row is valid. To see only the rows that are valid during a specific period, use the WM_OVERLAPS operator.

3.10 SQL* Loader Support for Valid Times

You can use the SQL* Loader utility to perform bulk loading into version-enabled tables with valid time support. You can include a valid time period for each row. If you do not specify a valid time period for a row in the SQL*Loader data file, the row is loaded and the WM_VALID period is set as from the current time until changed.

For usage and reference information about the SQL*Loader utility, see Oracle Database Utilities.

You can use the valid_time_update_mode parameter to the CommitBulkLoading procedure to specify what happens when a row to be loaded has a valid time range that overlaps the valid time range of an existing row having the same primary key. The possible values for the valid_time_update_mode parameter are:

SEQUENCED: The bulk loaded row will be treated as a sequenced update of the existing rows with overlapping time ranges.
NON-SEQENCED: The bulk loaded row will be treated as a nonsequenced update of the existing rows with overlapping time ranges.
DISCARD: (the default): The bulk loaded row will be moved to the discards table.

3.11 Adding Valid Time Support to an Existing Table

You can add valid time support to an existing version-enabled table by using the AlterVersionedTable procedure. You can specify a valid time period to be set in the WM_VALID column of all existing rows, or you can accept the default period of the current timestamp until changed.

Example 3-15 creates a table named MY_TABLE, version-enables it without valid time support, and then adds valid time support. After the valid time support is added, the WM_VALID column contains the default valid time period.

Example 3-15 Adding Valid Time Support to an Existing Version-Enabled Table

CREATE TABLE my_table (id NUMBER PRIMARY KEY);
EXECUTE DBMS_WM.EnableVersioning ('my_table');
INSERT INTO my_table VALUES (1);
SELECT * FROM my_table;

        ID
----------
         1

EXECUTE DBMS_WM.AlterVersionedTable('my_table', 'ADD_VALID_TIME');
SELECT * FROM my_table;

        ID
----------
WM_VALID(VALIDFROM, VALIDTILL)
--------------------------------------------------------------------------------
         1
WM_PERIOD('09-JUN-2003 10:04:13 -04:00', NULL)