I am developing a java app which can connect to oracle database and selecting column names from any tables, after selecting columns i have to query the data from those tables which the user select in my java app, now my question is how can i join all tables in the database so that query returns data successfully, i want to connect to any oracle schema to a specific, i will make the logic in java, but i am unable to find the query which can extract the data from all tables, i tried natural join among all tables but it has dependency of having same name of connecting columns. so i want to know any generic way which can work in all conditions.
As others have mentioned.. it seems that there are other tools out there that you probably should leverage prior to trying to roll your own complex solution.
With that said if you wish to roll your own solution you could look into using some of oracle's dictionary tables. Such as:
Select * from all_tables;
Select * from all_tab_cols;
Related
I have the following scenario and need to solve it in ORACLE:
Table A is on a DB-server
Table B is on a different server
Table A will be populated with data.
Whenever something is inserted to Table A, i want to copy it to Table B.
Table B nearly has similar columns, but sometimes I just want to get
the content from 2 columns from tableA and concatenate it and save it to
Table B.
I am not very familiar with ORACLE, but after researching on GOOGLE
some say that you can do it with TRIGGERS or VIEWS, how would you do it?
So in general, there is a table which will be populated and its content
should be copien to a different table.
This is the solution I came up so far
create public database link
other_db
connect to
user
identified by
pw
using 'tns-entry';
CREATE TRIGGER modify_remote_my_table
AFTER INSERT ON my_table
BEGIN INSERT INTO ....?
END;
/
How can I select the latest row that was inserted?
If the databases of these two tables are in two different servers, then you will need a database link (db-link) to be created in Table A schema so that it can access(read/write) the Table B data using db-link.
Step 1: Create a database link in Table A server db pointing to Table B server DB
Step 2: Create a trigger for Table A, which helps in inserting data to the table B using database link. You can customize ( concatenate the values) inside the trigger before inserting it into table B.
This link should help you
http://searchoracle.techtarget.com/tip/How-to-create-a-database-link-in-Oracle
Yes you can do this with triggers. But there may be a few disadvantages.
What if database B is not available? -> Exception handling in you trigger.
What if database B was not available for 2h? You inserted data into database A which is now missing in database B. -> Do crazy things with temporarily inserting it into a cache table in database A.
Performance. Well, the performance for inserting a lot of data will be ugly. Each time you insert data, Oracle will start the PL/SQL engine to insert the data into the remote database.
Maybe you could think about using MViews (Materialized Views) to replicate the data via database link. Later you can build your queries so that they access tables from database B and add the required data from database A by joining the MViews.
You can also use fast refresh to replicate the data (almost) realtime.
From perspective of an Oracle Database Admin this would make a lot more sense than the trigger approach.
try this code
database links are considered rather insecure and oracle own options are having licences associated these days, some of the other options are deprecated as well.
https://gist.github.com/anonymous/e3051239ba401e416565cdd912e0de8c
uses ora_rowscn to sync tables across two different oracle databases.
We have a legacy app that I am rewriting in .net. All of our databases are oracle and make use of database links. Is there any way for Entity Framework 6 to generate models based on tables located on a different database?
Currently the legacy app gets data from table like this
SELECT * FROM emp#foo2;
where its db connection is to database foo that has a database link to the database foo2.
I would like to reproduce this using EF6. So far all I have found regarding this is this question.
You can do two things that EF 4 or higher will work with:
CREATE VIEW EMP as SELECT * FROM emp#foo2;
CREATE MATERIALIZED VIEW EMP as SELECT * FROM emp#foo2;
LOBS are not accessible across a database link without some contorted PL/SQL processing to read the LOB piece by piece.
I believe fast refresh does not work across database links so you must consider the size of the table on the linked database. If you are refreshing a million rows you may find the time to do this is an issue. Most large tables are full of tombstone data that never changes so a timestamp column with the last modified date could help you create a package that only picks out the changed data.
If you are doing complicated joins for either ensure that Oracle considers the column that would be the primary key as not null.
You can add a primary key on views and materialized view but it must be disabled. See here for details.
I'm using Crystal Reports 2013 and have Oracle ODAC 32 and 64 bit versions installed. If I create a new report and use the "Oracle Server" data source, I can select from any tables to which I have access. However, I find I retrieve no data from some, not all, views.
The queries work fine in SQL Plus or SQL Developer. The queries retrieve data in Crystal Reports using outdated drivers like OLE DB and ODBC.
I can't find a commonality between the views that do or don't work. All the views I've tested with belong to the same schema. they all involve tables that belong to a third schema -- that is, I log in as USER1, query from a view belonging to USER2, which pulls data from tables belonging to USER2 and USER3. In order to create a view on a table and make that view available to others, Oracle requires SELECT WITH GRANT OPTION permission, which is in place. Again, the queries work fine in other SQL tools.
UPDATE: I've tried logging in as the owner of the views and was unable to query them. I've tried querying the underlying tables as the view owner (user2) and as the Crystal Reports owner (user1). Both users are able to query the underlying tables. The view itself seems to be the problem.
I'm studying the differences between the views that work and the views that don't work. I was optimistic when I found that the views that don't work were all using ORDER BY clauses that referenced column position (ex: ORDER BY 2, 1). I tried rewriting the ORDER BY to use column names. Didn't work. Tried removing the ORDER BY clauses. Didn't work. Back to the drawing board.
I found that the problem was that the Oracle view was using Oracle-specific, non-standard SQL. In addition to the ORDER BY 2, 1 mentioned above, there was an implicit date conversion in the WHERE clause e.g.
WHERE date_col = '01-JAN-2016'
When I added the TO_DATE function:
WHERE date_col = TO_DATE ('01-JAN-2016', 'dd-MON-yyyy')
Crystal Report was able to query the view.
I have a task to compare some Teradata Views with actual Oracle Tables.
I need a script for that.I have taken Java approach in which I connect to a specific schema from Oracle and then call the SELECT * FROM all_tables order by TABLE_NAME query and write this into a file.
I do the same for other schema but now my problem is Teradata.
Can you people please suggest me some script or query by which I can get proper details like it does with Oracle.
There is no complex Java Code but if you still want I can post it.
Edited:
Okay now I have a schema in Oracle which has all the tables.so views for those tables are created in Teredata.
I have to compare oracle tables and Teradata views every morning and send the differances.
So I use SELECT * FROM all_tables order by TABLE_NAME in Oracle and for Teradata I use SELECT * FROM dbc.tables WHERE tablekind='V' AND databasename='SCHEMA' order by TableName so now when I compare them I dont get accurate results, so I wanted to know does any script exists or how do I approach.
If your question is "How can I programmatically determine the structure of a view in Teradata?", then this should be a step in the right direction: HELP VIEW yourviewname;.
To get a list of views on a given table:
SELECT TableName
FROM DBC.Tables
WHERE Tablekind = 'V'
AND requestText LIKE '%yourtablename%'
GROUP BY 1
ORDER BY 1;
This information was gleaned from the official Teradata forums. You might also be interested in the Teradata users manuals. (Select your release version on the top right.)
I have two database connections in sql developer active lets say DB1 and DB2. I am working on ETL validation. So I want to check if data from Table1 of DB1 is populated correctly in Table2 of DB2.
To access tables from this two connections how can I write a query?
Any help on this will be helpful
There are common ways to validate if the ETL is correct:
You can run 2 queries to calculate the line counts separately against to Table1#DB1 and Table2#DB2, and compare the line counts between them.
Or perform some aggregate functions, such as sum(), avg()...etc on tables in DB1/DB2.