Problem: I have a table to which a customer may add columns. This table might have hundreds of columns of varying data types depending on how insane the customer is. I need to deploy an AFTER UPDATE trigger against this table to insert a row in another table for each column value that has changed.
Example:
Table_A, Row 1: Key_Value=1, Col1=123, Col2="foo"...Coln="bar"
becomes
Table_B, Row 1: Key_Value=1, ColName="Col1", ColValue=123
Table_B, Row 2: Key_Value=1, ColName="Col2", ColValue="foo"
Table_B, Row 3: Key_Value=1, ColName="Coln", ColValue="bar"
Since I do not know what columns they may create and this trigger must be deployed with the application, I need to evaluate the OLD vs NEW pseudo records dynamically (if :new.columns[1] != :old.columns[1] then...) to see what has changed and log only the changed columns. The only examples I have been able to find require referencing the columns in the pseudo records explicitly (if :new.col1 != :old.col1 then...).
Question: Is there a way to do this in Oracle?
Caveats: No, this is not for auditing purposes, so I cannot use Oracle's built-in auditing. No, we are not going to rewrite our app because you know how to do it better, this is the way it needs to work for better or worse.
Any helpful comments are welcome. All snarkey DBA drivel is not. Thanks in advance.
No. You can't dynamically reference columns in the :new or :old pseudorecord.
The closest you're likely to come is to write code that dynamically generates the entire trigger body by querying the data dictionary and making static references to columns in the pseudorecord. That code, however, would need to be run every time a column was added or removed from the table. Normally, that would be done as part of normal release management. If you are saying that people are adding and removing columns from this table without going through a release process, you could write a DDL trigger that submitted a job via dbms_job that called the procedure that rebuilt the trigger. That would be a lot of moving pieces and it would be a pain to troubleshoot when something inevitably goes wrong but if you're not open to alternate ways of implementing the functionality, that's complexity you'll have to live with.
Related
Let's say I created a table test_table in development just to test a trigger, this trigger would then be reused in many other tables (future and existing).
So I code the trigger, test it, all good! But at the moment, if I want to replicate it, I will have to copy it from test_table's triggers and edit it.
So if someone deletes the table accidentally, the trigger is gone, and I don't have it saved nowhere else. Or if I just want to delete random test tables in our database, I can't.
What's a recommended way to save a trigger as a "template" in oracle? So I can reuse it in other tables and have it not be dependant of a random test table, or any table.
There are a lot of ways you can keep a copy of your TRIGGER SQLText.
Here's a few examples.
In Version Control:
You can use any of the many version control tools to maintain a versioned history for any code you like, including SQL, PL/SQL, etc. You can rewind time, view differences over time, track changes to the template, even allow concurrent development.
As a Function:
If you want the template to live in the database, you can create a FUNCTION (or PACKAGE)that takes as parameters the target USER and TABLE, and it replaces the USER and TABLE values in its template to generate the SQLTEXT required to create or replace the template TRIGGER on the target TABLE. You can make it EDITIONABLE as needed.
In a Table:
You can always just create a TABLE that holds template TRIGGER SQLText as a CLOB or VARCHAR2. It would need to be somewhere where it isn't likele to be "randomly" deleted, though. You can AUDIT changes to the TABLE's data, to see the template change over time. Oracle has tons of auditing options.
In the logs:
You can just log (all) DDL out. If you ENABLE_DDL_LOGGING, the log xml will have a copy of every DDL statement, categorized, along with when and where it came from.
I have two procedures that I want to run on the same table, one uses the birth date and the other updates the name and last name taken from a third table.
The one that uses the birthday to update the age field runs all over the table, and the one that updates the names and last name only updates the rows that appear on the third table based on a key.
So I launched both and got deadlocked! Is there a way to prioritize any of them? I read about the nowait and skip locked for the update but then, how would I return to the ones skipped?
Hope you can help me on this!!
One possibility is to lock all rows you will update at once. Doing all updates in a single update statment will accomplish this. Or
select whatever from T
where ...
for update;
Another solution is to create what I call a "Gatekeeper" table. Both procedures need to lock the Gatekeeper table in exclusive mode before updating the table in question. The second procedure will block until the first commits but won't deadlock. In 11g you can create a table with no space allocated.
A variation is to insert a row in the Gatekeeper. Then lock only that row with select for update. Then you can use the Gatekeeper in other situations.
I would guess that you got locked because the update for all the rows and the update for a small set of rows accessed rows in different orders.
The former used a full scan and reached Raw A first, then went on to other rows, eventually trying to lock Row B. However, the other query was driven from an index or a join and already had Row B locked, and was off to lock Row A when it found it was already locked.
So, the fix: firstly, having an age column that needs to be constantly modified is a really bad idea. Perhaps it was done to allow indexing of age, but with a correctly written query an index on date of birth will let you find the same records just as quickly. You've broken normalisation rules and ended up coding yourself a deadlocking application. Hopefully you are only updating the rows that need to be updated, not all of them regardless -- I mean, that would just be insane.
The best solution is to get rid of that design flaw.
The not so good solution is to deconflict your queries by running them at different times or by using DBMS_Lock so that only one of them can run at any time.
Background: My team has an etl job that updates an aggregate table. Each row contains data for a particular date, but this row can and will get updated after the row date (which means any row can contain data from multiple jobs). This ETL job missed some data for one day last week and now I need to backfill it.
Problem: I have the missing data, and what I was planning on doing was dumping that data into a temporary table and then merging it with the agg table. That way I can deal with whether the ETL job already contains a row for that data (update) or whether a new row needs to be added (insert), but I don't have sufficient permissions to create a temp table, and I'd prefer not to involve the DBA.
Question: Can I do an insert/update sort of behavior without creating a temporary table (this is Oracle SQL by the way).
Edit: The data is coming from a tsv file.
Why do you want to avoid involving the DBA? The DBA should have full knowledge of what's going on in the database, as they are ultimately responsible for the condition of the data within it. So you shouldn't be playing sneaky commando with them.
As you have a file of missing data, the easiest way to present it to the database is with an external table. This requires the creation of the table and probably a directory object as well. You will need the DBA's help with this task.
The only way to avoid creating database objects is to convert your TSV file into a series of DML statements. An IDE which supports regex and/or records macros will prove invaluable here. I like TextPad; other editors are available.
The DML statement for doing upserts in Oracle is the MERGE statement. The one thing you need to watch for is recency. Your missing data comes from last week. If a row exists it may have have been added or amended in the intervening period. You must write your MERGE statement so it does not overwrite more recent data with the older stuff. Hopefully your table has useful metadata columns such as DATE_CREATED and LAST_UPDATED.
I have two tables tabA and tabB, that are identical.
I want to create a mechanism that for each time a new row is inserted into
tabA the row shall also "automatically" be inserted into rowB. If rows are deleted
in tabA, nothing shall happen in tabB.
I have used insert triggers for this but have had some problems. I have also got some
comments that triggers should not be used for this.
So, what should I use? Materialized views demands that tabA and tabB are the same.
In a perfect world one would strive to isolate table changes to a single program unit in order to uniformly apply business logic requirements such as this without impact to existing code that is driving the inserts. That said, many times this is not the best solution in practice, due to scattered inserts throughout an application. In that case, while not optimal, an insert trigger could easily be seen as the most pragmatic solution.
You could write a stored procedure that accepts the column values as parameters, and then applies an INSERT to both tabA and tabB.
I have two databases with identical table layouts. There are a dozen or so tables of interest. They are a number of FK between them.
I have been asked to write a stored procedure to copy data from database A to database B based on the PK of the parent table at the top of the hierarchy. I may receive just one value, or a list of values. I'm supposed to select all records from database A that match the value(s) and insert/update them into database B. This includes all the records in the child tables too.
My questions is whats the best(most efficent/ best practice) way to do this?
Should I write a dozen select from... insert into... statements?
Should I join the tables together an try to insert into all the tables at the same time?
Thanks!
Additional info:
The record should be inserted if it is not already there. (based on the PK of the respective table). Otherwise it should be updated.
Obviously I need to traverse down to all child tables, so There would only be one record to copy in the parent table, but the child table might have 10, and the child's child table might have 500. I would of course need to update the record if it already existed, insert if it does not for the child tables too...
UPDATE:
I think it would make the solution simpler if I just deleted all records related to the top level key, and then insert all the new records rather than trying to do updates.
So I guess the questions is it best to just do a dozen:
delete from ... where ... in ...
select from ... where ... in ...
insert into...
or is it better to do some kinda of fancy joins to do all the inserts in one sql statement?
I would do this by disabling all the foreign key constraints, then doing a set of MERGE statements to deal with the updates and inserts, then enable all the constraints.
Think about logging. How much redo do you want to generate?
You might find that it's quicker and better to truncate all the target tables and then do inserts of everything with nolog. Could be simpler than the merges.
One major main alternative would be to drop all the target tables and use export and import. Might be a lot faster.
A second alternative would be to use materialized views, particularly if you don't need to do updates on the target tables. That way, Oracle does all the heavy lifting for you. You can force integrity by choosing refresh groups carefully.
There are several ways to deal with this business problem. A PL/SQL program may not be the best.