Purpose
Deletes one or more rows from valid-time tables with the option of deleting the rows for only a portion of their valid-time periods.
Syntax
|
Syntax Element |
Description |
|
valid_time_table |
The valid-time table from which you are deleting rows. |
|
FOR PORTION OF |
Qualifies rows for deletion that have valid-time periods that are within or that overlap the period defined by point_in_time_1 and point_in_time_2. |
|
valid_time_period_name |
The name of the valid-time derived period column. This is not “VALIDTIME.” It is the name assigned to the derived period column when the table was defined. |
|
point_in_time_1 |
Delimits the period of applicability of the deletion. A date or timestamp expression that can be a constant, scalar UDF, scalar subquery, or business calendar function that evaluates to a DATE or TIMESTAMP[(n)] [WITH TIME ZONE] value. The expression can be any expression, including parameterized values and built-in functions such as CURRENT_DATE, CURRENT_TIMESTAMP, TEMPORAL_DATE, or TEMPORAL TIMESTAMP. The expression cannot reference any columns, but it can be a self-contained noncorrelated scalar subquery. |
|
WHERE search_condition |
For information on the this syntax and other nontemporal keywords, clauses, and options for DELETE, see SQL Data Manipulation Language. |
ANSI Compliance
This is ANSI SQL:2011 compliant.
Usage Notes
You cannot use the FOR PORTION OF qualifier within a MERGE INTO statement.
Examples of Deleting Rows from Valid-Time Tables
For the following examples, assume the queries are issued against the following valid-time table named employee_vt that contains a mix of current, future, and history rows:
eid ename terms job_start job_end
---- ----- ----- ---------- -----------
1002 Ash TA05 2003/01/01 2003/12/31
1005 Alice TW11 2004/12/01 2005/12/01
1010 Mike TW07 2015/01/01 2016/12/31
1005 Alice PW11 2005/12/01 9999/12/31
1001 Sania TW08 2002/01/01 2006/12/31
1004 Fred PW12 2001/05/01 9999/12/31
1003 SRK TM02 2004/02/10 2005/02/09
Example : Simple DELETE on an ANSI Valid-Time Table
A simple DELETE statement without temporal qualification operates just as a DELETE on a nontemporal table, completely deleting rows that qualify for deletion:
DELETE FROM employee_vt WHERE ename=’Ash’;
SELECT * FROM employee_vt;
eid ename terms job_start job_end
---- ----- ----- ---------- -----------
1005 Alice TW11 2004/12/01 2005/12/01
1010 Mike TW07 2015/01/01 2016/12/31
1005 Alice PW11 2005/12/01 9999/12/31
1001 Sania TW08 2002/01/01 2006/12/31
1004 Fred PW12 2001/05/01 9999/12/31
1003 SRK TM02 2004/02/10 2005/02/09
Example : Delete from an ANSI Valid-Time Table Where PA of Deletion is Within PV of Row
Temporal tables allow you to “delete” rows for only a portion of their period of validity. Teradata Database takes care of adding rows and adjusting valid-time periods to account for the change automatically. Teradata Database automatically handles the valid-time modifications for the row, which may involve changing the period bounds and adding new rows to the table.
For example, assume the company grants Fred a year off from his job in 2009. Deleting the Fred row for only that portion of the row period of validity automatically yields two rows for Fred in the table:
DELETE FROM employee_vt
FOR PORTION OF job_dur FROM DATE’2009-01-01’ TO DATE’2010-01-01’
WHERE ename=’Fred’;
SELECT * FROM employee_vt WHERE ename=’Fred’;
eid ename terms job_start job_end
---- ----- ----- ---------- -----------
1004 Fred PW12 2001/05/01 2009/01/01
1004 Fred PW12 2010/01/01 9999/12/31
Note: Even though this was a DELETE operation, the net effect was to add a row to the table.
Example : Delete from an ANSI Valid-Time Table where PA of Deletion Overlaps PV of Row
If the PV of the deletion overlaps the PA of a row, only the portion of the row information that is valid during the overlap is deleted, effectively changing the valid-time period for the row:
DELETE FROM employee_vt
FOR PORTION OF job_dur FROM DATE’2000-01-01’ TO DATE’2002-01-01’
WHERE ename=’Fred’;
SELECT * FROM employee_vt WHERE ename=’Fred’;
eid ename terms job_start job_end
---- ----- ----- ---------- -----------
1004 Fred PW12 2002/02/01 2009/01/01
1004 Fred PW12 2010/01/01 9999/12/31
DELETE FROM employee_vt
FOR PORTION OF job_dur FROM DATE’2008-05-05’ TO DATE’2009-05-05’
WHERE ename=’Fred’;
SELECT * FROM employee_vt WHERE ename=’Fred’;
eid ename terms job_start job_end
---- ----- ----- ---------- -----------
1004 Fred PW12 2002/01/01 2008/05/05
1004 Fred PW12 2009/05/01 9999/12/31