Long time user, first time "asker".
I am attempt to construct an Oracle procedure and/or trigger that will compare two tables with the MINUS operation and then insert any resulting rows into another table. I understand how to do the query in standard SQL, but I am having trouble coming up with an efficient way to do this using PL/SQL.
Admittedly, I am very new to Oracle and pretty green with SQL in general. This may be a silly way to go about accomplishing my goal, so allow me to explain what I am attempting to do.
I need to create some sort of alert that will be triggered when the V_$PARAMETER view is changed. Apparently triggers can not respond to changes to view but, instead, can only replace actions on views...which I do not wish to do. So, what I did was create a table that to mirror that view to essentially save it as a "snapshot".
create table mirror_v_$parameter as select * from v_$parameter;
Then, I attempted to make a procedure that would minus these two so that, whenever a change is made to v_$parameter, it will return the difference between the snapshot, mirror_v_$parameter. I trying to create a cursor with the command:
select * from v_$parameter minus select * from mirror_v_$parameter;
to be used inside a procedure, so that it could be used to fetch any returned rows and insert them into another table called alerts_v_$parameter. The intent being that, when something is added to the "alert" table, a trigger can be used to somehow (haven't gotten this far yet) notify my team that there has been a change to the v_$parameter table, and that they can refer to alerts_v_$parameter to see what has been change. I would use some kind of script to run this procedure at a regular interval. And maybe, some day down the line when I understand all this better, manipulate what goes into the alerts_v_$parameter table so that it provides better information such as specifically what column was changed, what was its previous value, etc.
Any advice or pointers?
Thank you for taking the time to read this. Any thoughts will be very appreciated.
I would create a table based on the exact structure of v_$parameter with an additional timestamp column for "last_update", and periodically (via DBMS_Scheduler) merge into it any changes from the real v_$parameter table and capture the timestamp of any detected change.
You might also populate a history table at the same time, either using triggers on update of your table or with SQL.
PL/SQL is unlikely to be required, except as a procedural wrapper to the SQL code.
Examples of Merge are in the documentation here: http://docs.oracle.com/cd/E11882_01/server.112/e26088/statements_9016.htm#SQLRF01606
Related
I am using sequences to create IDs, so while executing insert stored procedure it will create unique value for ID. But after some time it is losing the definition for the sequence.
Not sure why this is happening again and again and how to solve the problem?
I am using Oracle SQL Developer and in the edit table property there is 'Identity Column' setting. See below:
Next step is setting up trigger and sequence:
It was working fine for some time until this property defaulted. Now it is not there anymore:
Still have this trigger and sequence object in the schema and able to setup again but it will break later.
How to avoid this problem in future?
I think it is just a bug/limitation in your client software, Oracle SQL Developer. The "Identity Column" tab is a handy way to create the corresponding sequence and trigger but it doesn't seem to recognise existing elements. I've just verified my own system and that's exactly what happens.
It makes sense, because adding a new sequence and trigger is a pretty straightforward task (all you need is a template) but displaying current sequence is hard given that a trigger can implement any conceivable logic. Surely it could be done but the cost-benefit ratio probably left things this way.
In short, your app is not broken so nothing needs to be fixed on your side.
This is what I received from IT support regarding the issue:
A few possibilities that might cause this:
1 - Another user with limited privileges might be editing the table using SQL Developer. In this case, if this user's privilege is not enough to obtain the sequence and/or trigger information from the database, the tool might leave the fields blank and disable it when table changes are saved.
2 - The objects are being changed or removed outside of SQL Developer, causing it to lose the information. In my tests I noticed that dropping the trigger and recreating it with the same name caused the identity property information to be lost on SQL Developer.
Even being the trigger enabled, and working for inserts it could not retrieve the information.
Then, if I run an alter trigger to enable it (even tough dba_trigger is reporting it as already enabled), SQL Developer will list the information again:
ALTER TRIGGER "AWS"."TABLE1_TRG" ENABLE;
So it looks like there are some issues with the SQL Developer, that is causing this behavior.
Next time it happen, please check if the trigger still exist on the database and is enabled with the query below:
select owner, trigger_name, TRIGGER_TYPE, TRIGGERING_EVENT, TABLE_OWNER, TABLE_NAME, STATUS
from dba_triggers
where trigger_name = 'ENTER_YOUR_TRG_NAME'; --Just change the trigger name in WHERE
Lets suppose I created one table--
Create table t1 (aa varchar2(5),bb varchar2(5),cc varchar2(5));
Inserted values in it--
insert into T1 values ('a','b','c');
commit;
Now in one scenario, if i wanted to update all columns with same value then I am doing by this way--
UPDATE T1 SET AA='x',BB='x',CC='x';
Is there any another way by which this update task can be accomplished considering in real time there may be quite large number of columns and all has to be updated with same value in one go?
I am using Oracle 11.2.0.1.0 - 64bit Production
Note: Usually there are very less any scenarios where same values are being updated for all columns. But for example consider a school database and a good student scores 10/10 marks in all subjects. :-)
Thanks.
There is no way to do it in pure SQL. You must list down all the columns explicitly in the UPDATE statement.
And, believe me it is not a difficult task using a good text editor. Using the metadata you could get the list of column names in few seconds, all you need to do is prepare the SQL statement as per the syntax.
If you really want to do it dynamically, then you need to do it in PL/SQL and (ab)use EXECUTE IMMEDIATE. I would personally not suggest it unless you are just doing it for learning purpose.
You could try this:
UPDATE T1 SET AA='x',BB=AA,CC=AA;
I have a trigger that calls a stored procedure when activated, passing :NEW values as a parameter. I have about 40 tables that use the same trigger, and I would like to use the same code for each trigger. Therefore, I am trying to pass all columns of a new row. My code is below and shows what I am attempting to do (however, the problem is that :NEW.* is not a valid expression):
CREATE OR REPLACE TRIGGER "TRIG_TEST_TRIGGER"
AFTER INSERT OR DELETE OR UPDATE ON TRIG_TEST
FOR EACH ROW
DECLARE
BEGIN
MY_STORED_PROC('Trigger Activated: ' || :NEW.*);
END;
Most likely, you can't.
You could write a procedure that uses dynamic SQL to generate the appropriate trigger code for each table. Of course, that would require that you re-run the procedure to re-create the trigger every time the table changes.
I'm a bit hard-pressed, though, to imagine what my_stored_proc might be doing that it would make sense to pass it a string representing every column from 1 of 40 tables with, presumably, 40 different sets of columns. If you're writing to a log table, if you want the data from every column, that generally implies that you want to be able to see the evolution of a particular row over time. But that is extremely hard to do if your log table just has strings in all sorts of different formats from many different tables since you'd constantly have to do things like parsing the string that you logged.
Apex beginner here. I have a view in my Oracle database of the form:
create or replace view vw_awkward_view as
select unique tab1.some_column1,
tab2.some_column1,
tab2.some_column2,
tab2.some_column3
from table_1 tab1,
table_2 tab2
WHERE ....
I need the 'unique' clause on 'tab1.some_column1' because it has many entries in its underlying table. I also need to include 'tab1.some_column1' in my view because the rest of the data doesn't make much sense without it.
In Apex, I want to create a report on this view with a form for editing it (update only). I do NOT need to edit tab1.some_column1. Only the other columns in the view need to be editable. I can normally achieve this using an 'instead-of' trigger, but this doesn't look possible when the view contains a 'distinct', 'unique' or 'group by' clause.
If I try to update a row on this view I get the following error:
ORA-02014: cannot select FOR UPDATE from view with DISTINCT, GROUP BY, etc.
How can I avoid this error? I want my 'instead-of' trigger to kick in and perform the update and I don't need to edit the column which has the 'unique' clause, so I think it should be possible to do this.
I think that you should be able to remove the "unique".
if tab2.some_column1, tab2.some_column2, tab2.some_column3 are not unique, then how do you want to update them ?
if they are unique then the whole result: tab1.some_column1, tab2.some_column1, tab2.some_column2, tab2.some_column3 is unique.
When you state in a sql query "unique" or "distinct" it's for all columns not only 'tab1.some_column1'
Hope i'm in the correct direction of your question here ;)
Your query could be achieved by doing something like:
select a.some_column1, tab2.some_column1, tab2.some_column2, tab2.some_column3
from table_2 tab2
join (select distinct some_column1 from table_1) a
on tab2.column_in_tab1 = a.some_column1
The reason you get the ORA-02014 error is because of the automatically generated ApplyMRU process. This process will attempt to lock a (the) changed row(s):
begin
for r in (select ...
from vw_awkward_view
where <your first defined PK column>= 'value for PK1'
for update nowait)
loop
null;
end loop;
end;
That's a bummer, and means you won't be able to use the generated process. You'll have to write your own process which does the updating.
For this, you'll have to use the F## arrays in apex_application.
If this sounds totally unfamiliar, take a look at:
Custom submit process, and on using the apex_application arrays.
Also, here is a how-to for apex from 2004 from Oracle itself. It still uses lots of htmldb references, but the gist of it is there.
(it might be a good idea to use the apex_item interface to build up your form, and have control over what is generated and what array it takes.)
What it comes down to is: loop over the array containing your items and do an UPDATE on your view with the submitted values.
Of course, you don't have locking this way, nor a way to prevent unnecessary updates.
Locking you can do yourself, with for example using the select for update method. You'd have to lock the correct rows in the table(s) you want to alter, before you update them. If the locking fails, then your process should fail.
As for the 'lost update' story: here you'd need to check the MD5-checksums. A checksum is generated from the editable columns in your form and put in the html-code. On submit, this checksum is then compared to a newly generated checksum from those same columns, but with values from the database at that time of submit. If the checksums differ, it means the record has changed between the page load and the page submit. Your process should fail because the record has been altered, and you don't want to have those overwritten. (if you go the apex_item way, then don't forget to include an MD5_CHECKSUM call (or MD5_HIDDEN).
Important note though: checksums generated by either using apex_item or simply the standard form functionality build up a string to be hashed. As you can see in apex_item.md5_hidden, checksums are generated using DBMS_OBFUSCATION_TOOLKIT.MD5.
You can get the checksum of the values in the DB in 2 ways: wwv_flow_item.md5 or using dbms_obfuscation.
However, what the documentation fails to mention is this: OTN Apex discussion on MD5 checksums. Pipes are added in the generated checksums! Don't forget this, or it'll blow up in your face and you'll be left wondering for days what the hell is wrong with it.
Example:
select utl_raw.cast_to_raw(dbms_obfuscation_toolkit.md5(input_string=>
"COLUMN1" ||'|'||
"COLUMN2" ||'|'||
"COLUMN5" ||'|'||
"COLUMN7" ||'|'||
"COLUMN10" ||'|'||
"COLUMN12" ||'|'||
"COLUMN14" ||
'|||||||||||||||||||||||||||||||||||||||||||'
)) md5
from some_table
To get the checksum of a row of the some_table table, where columns 1,2,5,7,10,12,14 are editable!
In the end, this is how it should be structured:
loop over array
generate a checksum for the current value of the editable columns
from the database
compare this checksum with the submitted checksum
(apex_application.g_fcs if generated) if the checksums match,
proceed with update. If not, fail process here.
lock the correct records for updating. Specify nowait, and it
locking fails, fail the process
update your view with the submitted values. Your instead-of trigger
will fire. Be sure you use correct values for your update statement so that only this one record will be updated
Don't commit inbetween. It's either all or nothing.
I almost feel like i went overboard, and it might feel like it is all a bit much, but when you know the pitfalls it's actually not so hard to pull this custom process off! It was very knowledgable for me to play with it :p
The answer by Tom is a correct way of dealing with ths issue but I think overkill for your requirements if I understand correctly.
The easiest way may be to create a form on the table you want to edit. Then have the report edit link take the user to this form which will only update the needed columns from the one table. If you need the value of the column from the other table displayed it is simple when you create the link to pass this value to the form which can contain a display only item to show this.
Can I find out when the last INSERT, UPDATE or DELETE statement was performed on a table in an Oracle database and if so, how?
A little background: The Oracle version is 10g. I have a batch application that runs regularly, reads data from a single Oracle table and writes it into a file. I would like to skip this if the data hasn't changed since the last time the job ran.
The application is written in C++ and communicates with Oracle via OCI. It logs into Oracle with a "normal" user, so I can't use any special admin stuff.
Edit: Okay, "Special Admin Stuff" wasn't exactly a good description. What I mean is: I can't do anything besides SELECTing from tables and calling stored procedures. Changing anything about the database itself (like adding triggers), is sadly not an option if want to get it done before 2010.
I'm really late to this party but here's how I did it:
SELECT SCN_TO_TIMESTAMP(MAX(ora_rowscn)) from myTable;
It's close enough for my purposes.
Since you are on 10g, you could potentially use the ORA_ROWSCN pseudocolumn. That gives you an upper bound of the last SCN (system change number) that caused a change in the row. Since this is an increasing sequence, you could store off the maximum ORA_ROWSCN that you've seen and then look only for data with an SCN greater than that.
By default, ORA_ROWSCN is actually maintained at the block level, so a change to any row in a block will change the ORA_ROWSCN for all rows in the block. This is probably quite sufficient if the intention is to minimize the number of rows you process multiple times with no changes if we're talking about "normal" data access patterns. You can rebuild the table with ROWDEPENDENCIES which will cause the ORA_ROWSCN to be tracked at the row level, which gives you more granular information but requires a one-time effort to rebuild the table.
Another option would be to configure something like Change Data Capture (CDC) and to make your OCI application a subscriber to changes to the table, but that also requires a one-time effort to configure CDC.
Ask your DBA about auditing. He can start an audit with a simple command like :
AUDIT INSERT ON user.table
Then you can query the table USER_AUDIT_OBJECT to determine if there has been an insert on your table since the last export.
google for Oracle auditing for more info...
SELECT * FROM all_tab_modifications;
Could you run a checksum of some sort on the result and store that locally? Then when your application queries the database, you can compare its checksum and determine if you should import it?
It looks like you may be able to use the ORA_HASH function to accomplish this.
Update: Another good resource: 10g’s ORA_HASH function to determine if two Oracle tables’ data are equal
Oracle can watch tables for changes and when a change occurs can execute a callback function in PL/SQL or OCI. The callback gets an object that's a collection of tables which changed, and that has a collection of rowid which changed, and the type of action, Ins, upd, del.
So you don't even go to the table, you sit and wait to be called. You'll only go if there are changes to write.
It's called Database Change Notification. It's much simpler than CDC as Justin mentioned, but both require some fancy admin stuff. The good part is that neither of these require changes to the APPLICATION.
The caveat is that CDC is fine for high volume tables, DCN is not.
If the auditing is enabled on the server, just simply use
SELECT *
FROM ALL_TAB_MODIFICATIONS
WHERE TABLE_NAME IN ()
You would need to add a trigger on insert, update, delete that sets a value in another table to sysdate.
When you run application, it would read the value and save it somewhere so that the next time it is run it has a reference to compare.
Would you consider that "Special Admin Stuff"?
It would be better to describe what you're actually doing so you get clearer answers.
How long does the batch process take to write the file? It may be easiest to let it go ahead and then compare the file against a copy of the file from the previous run to see if they are identical.
If any one is still looking for an answer they can use Oracle Database Change Notification feature coming with Oracle 10g. It requires CHANGE NOTIFICATION system privilege. You can register listeners when to trigger a notification back to the application.
Please use the below statement
select * from all_objects ao where ao.OBJECT_TYPE = 'TABLE' and ao.OWNER = 'YOUR_SCHEMA_NAME'