I searched a bit and I found some info on how to call java code from database trigger but none about the opposite. Isn't it possible to call a trigger from a java method?
After inserting to one table (Table1), I need to create several rows to another table (Table2) from a select on the first one. I built the trigger but if I make it to execute after insert on the first table I get an error:
ORA-04091: table Table1 is mutating, trigger/function may not see it ORA-06512:....
I am working on an ADF application, and as Table1-Table2 have a master detail relationship, maybe it doesn't allow inserting rows this way. That is why I thought that calling the trigger through a button may solve my problem. Any idea?
Trigger:
CREATE OR REPLACE TRIGGER Table2
AFTER INSERT ON Table1 REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
BEGIN
insert into Table2
(
Select col1,col2... from Table1
);
END;
Triggers can't be called directly, they are only executed before/after rows are inserted/updated/deleted.
The problem is that in your trigger you are trying to access the table for which you have created your trigger, and that results in the mutating trigger error, because the trigger won't see the changes in the table.
Can you show use the code of your trigger? Why do you have to access that table? Maybe you could just use a stored procedure to achieve what you need and call it?
Edit
If you want to access the values from inserted row, you should just use the :new pseudorecord:
CREATE OR REPLACE TRIGGER Table2
AFTER INSERT ON Table1 REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
BEGIN
insert into Table2 values (:new.some_col, :new.some_col2, <other columns>);
END;
For calling your treatment you can create a PL/SQL Procedure/function and copy/paste (modulo some modifications) your trigger code in this procedure.
From what i understand, no insert should complete until the trigger has been completed perhaps there is an issue with the insert statement?
Related
I am using Hibernate with MSSQL server writing the software that integrates with an existing database. There is an instead of insert trigger on the table that I need to insert into and it messes up ##Identity, which means on Hibernate's save I can't get the id of inserted row. I can't control the trigger (can't modify it). I saw this question, but it involves procedures, which my trigger does not have, so I thought my question is different enough. I can't post the whole trigger, but hopefully I can post enough to get the point across:
CREATE TRIGGER TrigName ON TableName
INSTEAD OF INSERT
AS
SET XACT_ABORT ON
BEGIN TRANSACTION
-- several DECLARE, SET statements
-- a couple of inserts into other tables for business logic
-- plain T-SQL statements without procedures or functions
...
-- this is the actual insert that i need to perform
-- to be honest, I don't quite understand how INSERTED table
-- was filled with all necessary columns by this point, but for now
-- I accept it as is (I am no SQL pro...)
INSERT INTO ClientTable (<columns>)
SELECT <same columns> from INSERTED
-- a couple of UPDATE queries to unrelated tables
...
COMMIT TRANSACTION;
I was wondering if there is a reliable way to get the id of the row being inserted? One solution I thought of and tried to make is to install an on insert trigger on the same table that writes the newly inserted row into a new table I added to the db. I'd use that table as a queue. After transaction commit in Hibernate I could go into that table and run a select with the info I just inserted (I still have access to it from the same method scope), and I can get the id and finally remove that row. This is a bulky solution, but best I can come up with so far.
Would really appreciate some help. I can't modify existing triggers and procedures, but I can add something to the db if it absolutely does not affect existing logic (like that new table and a on insert trigger).
To sum up: I need to find a way to get the ID of the row I just inserted with Hibernate's save call. Because of that instead of insert trigger, hibernate always returns identity=0. I need to find a way to get that ID because I need to do the insert in a few other tables during one transaction.
I think I found an answer for my question. To reply to #SeanLange's comment: I can't actually edit insert code - it's done by another application and inquiry to change that will take too long (or won't happen - it's a legacy application). What I did is insert another trigger on insert on the same table. Since I know the order of operations in the existing instead of insert trigger I can see that the last insert operation will be in the table I want so that means my on insert trigger will fire right after that. In the scope of that trigger I have access to inserted table out of which I pull out the id.
CREATE TRIGGER Client_OnInsert ON myClientTable
FOR INSERT
AS
BEGIN
DECLARE #ID int;
SET #ID = (select ClientID from inserted);
INSERT INTO ModClient (modClientId)
OUTPUT #ID
VALUES (#ID);
END
GO
Then in Hibernate (since I can't use save() anymore), I use a NativeQuery to do this insert. I set parameters and run the list() method of NativeQuery, which returns a List where the first and only argument is the id I want.
This is a bulky way, I know. If there is anything that's really bad that will stand out to people - please let me know. I would really appreciate some feedback on this. However, I wanted to post this answer as a potential answer that worked so far, but it does not mean it's very good. For this solution to work I did have to create another small table ModClient, which I will have to use as a temp id storage for this exact purpose.
I would like to do a real time reading from mysql.
The idea is simple. I use the binary log to trigger the select statement.
Meanwhile I'd like to read only the new rows on every change.
And currently I just consider insert.
So when someone do
insert into sometable(uid,somecolumn) values(uid,something)
My code will be triggered and do
select from sometable where uid=uid
Of course I have already written down which columns are the primary key because it seems no information from binlog.
I cannot find a tool to analysis mysql insert statement. So I use the regex to find out which column equals which value, then extract primary keys.
BUT the real problems what will happen if I do
Insert into `table` (`col`) values (select 0 as `col` from `dummy`);
How can I find out the col=0?
Is it impossible that make a select statement that select the new changed rows, triggered by the insert statement?
In a TRIGGER, you have access to the OLD and NEW values. With them, you can write code (in the TRIGGER) to log, for example, just the changes. Something like...
IF NEW.col1 != OLD.col1 THEN INSERT INTO LOG ...; END;
IF NEW.col2 != OLD.col2 THEN INSERT INTO LOG ...; END;
I am implementing application specific data import feature from one database to another.
I have a CSV file containing say 10000 rows. These rows need to be inserted/updated into database.
I am using mysql database and inserting from Java.
There might be the case, where couple of rows may present in database that means those need to be updated. If not present in database, those need to be inserted.
One possible solution is that, I can read one by one line, check the entry in database and build insert/update queries accordingly. But this process may take much time to create update/insert queries and execute them in database. Some times my CSV file may have millions of records.
Is there any other faster way to achieve this feature?
I don't know how you determine "is already present", but if it's any kind of database level constraint (probably on a primary key?) you can make use of the REPLACE INTO statement, which will create a record unless it gets an error in which case it'll update the record that prevents it from being inserted.
It works just like INSERT basically:
REPLACE INTO table ( id, field1, field2 )
VALUES ( 1, 'value1', 'value'2 )
If a row with ID 1 exists, it's updated with these values; otherwise it's created.
Given that you're using MySQL you could use the INSERT ... ON DUPLICATE KEY UPDATE ... statement, which functions similarly to the SQL standard MERGE statement. MYSQL doc reference here and general Wikipedia reference to SQL MERGE functionality here. The statement would look something like
INSERT INTO MY_TABLE
(PRIMARY_KEY_COL, COL2, COL3, COL4)
VALUES
(1, 2, 3, 4)
ON DUPLICATE KEY
UPDATE COL2 = 2,
COL3 = 3,
COL4 = 4
In this example I'm assuming that PRIMARY_KEY_COL is a primary or unique key on MY_TABLE. If the INSERT statement would fail due to a duplicate value on the primary or unique key then the UPDATE clause is executed. Also note (on the MySQL doc page) that there are some gotcha's associated with auto-increment columns on an InnoDB table.
Share and enjoy.
Do you need to do this often or just once in a while?
I need to load csv files from time to time to a database for analysis and I created a SSIS-Datasolution with a Data Flow task which loads the csv-File into a table on the SQL Server.
For more infos look at this blog
http://blog.sqlauthority.com/2011/05/12/sql-server-import-csv-file-into-database-table-using-ssis/
Add a stored procedure in SQL for inserting. In the stored procedure use a try catch block to do the insert. If the insert fails do an update. Then you can simply call this method from your program.
Alternatively:
UPDATE Table1 SET (...) WHERE Column1='SomeValue'
IF ##ROWCOUNT=0
INSERT INTO Table1 VALUES (...)
Sorry if my question is not specific or if it has been answered before. I tried looking for it and for a better way to ask but this is the most accurate way.
I have developed a program in Java in which I insert a new row into my database in the following way:
INSERT INTO table_name VALUES (?,?,?)
The thing is that I have this query in many parts of the program, and now I decided to add a fourth column to my table. Do I have to update EVERY SINGLE query with a new question mark in the program? If I dont, it crashes.
What is the best way to proceed in these cases?
YES.
you need to add extra ? (parameter placeholder) because you are using implicit INSERT statement. That means that you didn't specify the column names of the table to which the values will be inserted.
INSERT INTO table_name VALUES (?,?,?)
// the server assumes that you are inserting values for all
// columns in your table
// if you fail to add value on one column. an exception will be thrown
The next time you create an INSERT statement, make sure that you specify the column names on it so when you alter the table by adding extra column, you won't update all your place holders.
INSERT INTO table_name (Col1, col2, col3) VALUES (?,?,?)
// the server knows that you are inserting values for a specific column
Do I have to update EVERY SINGLE query with a new question mark in the program?
Probably. What you should do, while you're updating every single one of those queries, is to encapsulate them into an object, probably using a Data Source pattern such as a Table Data Gateway or a Row Data Gateway. That way you Don't Repeat Yourself and the next time you update the table, you only have one place to update the query.
Because of the syntax you've used, you might run some issues. I've referring to the lack of column names. Your INSERT queries will start failing as soon as you change your table structure.
If you had used the following syntax:
INSERT INTO table_name (C1, C2, C3) VALUES (?,?,?)
assuming your new column has a proper default value, then it would've work fine.
I have a program that has 2 threads running, and each thread has its own database JDBC connection, and they will access/modify the same database table A like below. Table A only has 2 columns (id, name), and the primary key is the combination of id and name.
statement stmt;
// first delete it if the record has exist in table
stmt.addBatch("delete from A where id='arg_id' and name='arg_name';");
// then insert it to table
stmt.addBatch("insert into A values (arg_id, arg_name);");
stmt.executeBatch();
The 2 threads maybe insert the same data to the table, and i got the following exception,
java.sql.BatchUpdateException: Duplicate entry '0001-joey' for key 1
at com.mysql.jdbc.Statement.executeBatch(Statement.java:708)
at com.mchange.v2.c3p0.impl.NewProxyStatement.executeBatch(NewProxyStatement.java:743)
at proc.Worker.norD(NW.java:450)
Do you have any idea how I can fix this issue? Thank you.
Regards,
Joey
Why not introduce a simple optimistic locking mecanism on the database?
Add a version column and track the version number when performing delete or update transactions.
Your table would look like
create table test(
id int not null primary key,
name varchar,
rowversion int default = 0);
Every time you retrieve a row you should retrieve the row version so you can do
update test set name='new name' rowversion=rowversion+1 where id=id and rowversion=retrieved row version;
The same with delete
delete from test where id=id and rowversion=retrievedRowVersion;
This is a simple mechanism that will exploit the dbms concurency management features. Check this link for more information on optimistic locking http://en.wikipedia.org/wiki/Optimistic_concurrency_control#Examples
This is obviously only a very simple implementation of concurency management but your problem has to take these into account.
Also for the double insert the fact that your transaction is rejected is good that means that no duplicate keys are inserted. You should just handle the Exception and notify the user of what happen.
Wrap both statements in a transaction:
BEGIN;
DELETE FROM a WHERE ...;
INSERT INTO a VALUES (...);
COMMIT;
Note that as long as the table consists of only the primary key, this conflict arises only when the table is unmodified at the end; I presume you want to add more columns, in which case you should use the UPDATE ... WHERE syntax to change values.
Are you using any kind of synchronization? First you will need to wrap the code that modifies the table in:
synchronized(obj)
{
// code
}
where obj is an object that both threads can access.
I don't know the exact semantics of your table modifications, but if they both insert ids, you will also need to hold a "global" id and atomically increment it in each thread, such that they don't both get the same value.