问题
I've read the Oracle docs on creating triggers and am doing things exactly how it shows, however this just isn't working. My goal is to update the TPM_PROJECT table with the minimum STARTDATE appearing in the TPM_TRAININGPLAN table. Thus, every time someone updates the STARTDATE column in TPM_TRAININGPLAN, I want to update teh TPM_PROJECT table. Here's what I'm trying:
CREATE TRIGGER Trigger_UpdateTrainingDelivery
AFTER DELETE OR INSERT OR UPDATE OF STARTDATE
ON TPM_TRAININGPLAN
FOR EACH ROW WHEN (new.TRAININGPLANTYPE='prescribed')
BEGIN
UPDATE TPM_PROJECT SET TRAININGDELIVERYSTART = (SELECT MIN(TP.STARTDATE) FROM TPM_TRAININGPLAN TP WHERE TP.PROJECTID = new.PROJECTID AND TP.TRAININGPLANTYPE='prescribed')
WHERE PROJECTID = new.PROJECTID
END;
The trigger is created with no errors, but I do get a warning:
Warnings: --->
W (1): Warning: execution completed with warning
<---
Of course Oracle isn't nice enough to actually tell me what the warning is, I simply am shown that there is one.
Next, if I update the training plan table with:
UPDATE TPM_TRAININGPLAN
set STARTDATE = to_date('03/12/2009','mm/dd/yyyy')
where TRAININGPLANID=15916;
I get the error message:
>[Error] Script lines: 20-22 ------------------------
ORA-04098: trigger 'TPMDBO.TRIGGER_UPDATETRAININGDELIVERY' is invalid and failed re-validation
Script line 20, statement line 1, column 7
Any ideas what I'm doing wrong? Thanks!
回答1:
A few issues in no particular order.
First, in the body of a row-level trigger, you need to use :new and :old to reference the new and old records. The leading colon is necessary. So your WHERE clause would need to be
WHERE PROJECTID = :new.PROJECTID
Second, if you are running your CREATE TRIGGER in SQL*Plus, you can get a list of the errors and warnings using the SHOW ERRORS command, i.e.
SQL> show errors
You could also query the DBA_ERRORS table (or ALL_ERRORS or USER_ERRORS depending on your privilege level) but that's not something you normally need to resort to.
Third, assuming the syntax errors get corrected, you're going to get a mutating table error if you use this logic. A row level trigger on table A (TPM_TRAININGPLAN in this case) cannot query table A because the table may be in an inconsistent state. You can work around that, as Tim shows in his article, by creating a package with a collection, initializing that collection in a before statement trigger, populating the data in the collection in a row-level trigger, and then processing the modified rows in an after statement trigger. That's a decent amount of complexity to add to the system, however, since you'll have to manage multiple different objects.
Generally, you'd be better off implementing this logic as part of whatever API you use to manipulate the TPM_TRAININGPLAN table. If that is a stored procedure, it makes much more sense to put the logic to update TPM_PROJECT in that stored procedure rather than putting it in a trigger. It is notoriously painful to try to debug an application that has a lot of logic embedded in triggers because that makes it very difficult for developers to follow exactly what operations are being performed. Alternately, you could remove the TRAININGDELIVERYSTART column from TPM_PROJECT table and just compute the minimum start date at runtime.
Fourth, if your trigger fires on inserts, updates, and deletes, you can't simply reference :new values. :new is valid for inserts and updates but it is going to be NULL if you're doing a delete. :old is valid for deletes and updates but is going to be NULL if you're doing an insert. That means that you probably need to have logic along the lines of (referencing Tim's package solution)
BEGIN
IF inserting
THEN
trigger_api.tab1_row_change(p_id => :new.projectid, p_action => 'INSERT');
ELSIF updating
THEN
trigger_api.tab1_row_change(p_id => :new.projectid, p_action => 'UPDATE');
ELSIF deleting
THEN
trigger_api.tab1_row_change(p_id => :old.projectid, p_action => 'DELETE');
END IF;
END;
回答2:
As Justin Cave have suggested, you can calculate the minimum start date when you need it. It might help if you create an index on (projectid, startdate);
If you really have a lot of projects and training plans, another solution could be to create a MATERIALIZED VIEW that has all the data that you need:
CREATE MATERIALIZED VIEW my_view
... add refresh options here ...
AS
SELECT t.projectid, MIN(t.start_date) AS min_start_date
FROM TPM_TRAININGPLAN t
GROUP BY t.projectid;
(sorry, don't have Oracle running, the above code is just for the reference)
来源：https://stackoverflow.com/questions/7507636/oracle-problem-creating-trigger-that-updates-another-table