How to update multiple rows with the same sequence value - sql

Question

I'm using DB2 and want to update several rows that meet my condition with the same next value from my sequence.
Here is what I tried but this doesn't work as the next value is fetched for each row:-
update dependency dep set vid=NEXT VALUE FOR seq_VID where id in ('8371','8372','8373')
id is the the primary key and seq_VID is a sequence. So what I had hoped was that say the next sequence value was 99, that 99 would be set for all 3 rows (and not 99,100,101 as is the case with this).
My workaround is to break it into separate statements for each id in my list, i.e.
update dependency dep set vid=NEXT VALUE FOR seq_VID where id= ('8371')
update dependency dep set vid=PREVIOUS VALUE FOR seq_VID where id= ('8372')
update dependency dep set vid=PREVIOUS VALUE FOR seq_VID where id= ('8373')
But I'd like to execute this in one SQL statement if possible - any ideas?

Answer 1

If you always knew that you wanted to put the 'previous' sequence value on the two rows after the one you updated with the 'next' next value you might be able to use a compound trigger, similar to the following (Oracle syntax, please forgive):
CREATE OR REPLACE TRIGGER DEPENDENCY_COMPOUND
FOR UPDATE ON DEPENDENCY
COMPOUND TRIGGER
TYPE tDependency_row_table IS TABLE OF DEPENDENCY%ROWTYPE;
tblDependency_rows tDependency_row_table := tDependency_row_table();
AFTER EACH ROW IS
BEGIN
tblDependency_rows.EXTEND;
tblDependency_rows(tblDependency_rows.LAST).ID = NEW.ID+1;
tblDependency_rows(tblDependency_rows.LAST).VID = seq_VID.CURRVAL;
tblDependency_rows.EXTEND;
tblDependency_rows(tblDependency_rows.LAST).ID = NEW.ID+2;
tblDependency_rows(tblDependency_rows.LAST).VID = seq_VID.CURRVAL;
END;
AFTER STATEMENT IS
BEGIN
FOR i IN tblDependency_rows.FIRST..tblDependency_rows.LAST LOOP
UPDATE DEPENDENCY
SET VID = tblDependency_rows(i).VID
WHERE ID = tblDependency_rows(i).ID;
END LOOP;
END;
END DEPENDENCY_AU;
Then you'd issue your update statement as
UPDATE DEPENDENCY
SET VID = seq_VID.NEXTVAL
WHERE ID = 8371;
and the trigger should take care of updating the other two rows.
The compound trigger is useful in Oracle 11+ to help work around the 'mutating table' error, which occurs when a trigger attempts to SELECT, INSERT, UPDATE, or DELETE data in the same table which the trigger is on.
This is a rather contrived situation and makes some huge assumptions about which rows should be updated, but perhaps it will prove useful.
Share and enjoy.