In Exadata, I have two different databases.
Is it possible to perform a join between a table that is in database A, to a table that is in database B?
On the standard Oracle database engine, I know this is not possible except via a db-link but I have a doubt with Exadata... If anyone can give me any information !
DB Link is the way. Exadata is essentially a storage technology; so the fact that it's Exadata is irrelavant for this is question
Related
I have a MS SQL (SQL Server 2008) database with some data in it and a postgresql (9) database with other data. I need to do some queries to find related data. I know how to link two MS SQL databases together but not sure how to even start with the mixed database types.
The new company I work for has postgresql, I have not worked with it before. The guy I replaced was really the only one here who knew much about it. So no internal resources.
I'm not ready to build a solution in code at this point (.NET), just hoping to have a tool to do some queries.
Postgresql has table
Company
Company_id, Company_name, ....
MS SQL had table
Companies
company_name, postgresql_company_id, company_id, ....
If you ever need to run queries from Postgres that pulls data from SQL-Server, you can use foreign data wrappers. The ODBC driver should work fine:
http://wiki.postgresql.org/wiki/Foreign_data_wrappers
I'm not familiar enough with SQL-Server to give an authoritative answer on how to do it the other way around, but since Postgres speaks ODBC, I'm guessing it's close enough to how you make a SQL-Server talk with another one.
Related thread: SQL Server 2012: Add a linked server to PostgreSQL
I'm using MySQL workbench 5.2.35 CE to reverse a Mysql Database and show the diagram of tables with their relationships.
I am able to get every table and its fields but the relations between them is not shown. Why is that? Is there any way it can be fixed?
Most often, the relations between tables are not stored in the DB. How to combine two tables is entirely up to the SQL query and because there are near endless possibilities to name your columns this is not easy to guess. Try to find some SELECT statements or use brute force to find out wich columns match.
If you are using MyISAM as the database engine, your database is not fully relational. Make your database fully relational by using InnoDB engine. Then you will be able to see the relations when you do reverse engineering. But please note that each has pros and cons of its own. Google MyISAM vs InnoDB to find out more about the differences.
I have tested mysql-workbench for both 5.2 and 6.0 latest version. My database got foreign key constraints defined clearly. My database is using mysql-native SQL. But the relationships are shown as line between tables. I have created another test database with only two tables. In this case the InoDb was used as engine. The foreign key constrain clearly defined. Still it only generate two lonely table object in the ER diagram after going through the "reverse engineering" module.
While using another commercial software, I was able to generate the 'lines' between the Entities.
My question is, is this a problem of workbench itself, or some error on my part. My database server is the latest stable version 5.6.12. If I can get an answer, this will be good for everyone. You don't have to waste time trying to get an ER-diagram with this piece of software.
I have my project A with mySql database and I have another project B with msSql. I have connected the database from A and fetched data from B. But now I need to use inner join for tables in A and B. Is it possible to do so with databases in the same server and different server? Any help will be appreciated.
Thanks in advance
Yes, it should be possible. First, you will need to link your MySQL server to your MS SQL Server.
See this reference. Secondly, you will probably need to use sub queries to select the correct columns and do the join on them;
SELECT *
FROM
(SELECT ms_column1, ms_column2 FROM MSSQLTABLE) AS mssql
JOIN
(SELECT my_column1, my_column2
FROM openquery(LINKED_SERVER, 'SELECT column1, column2 FROM MYSQLTABLE') AS mysql
ON mssql.ms_column1 = mysql.my_column1
Unfortunately untested.
Instead of making the two different databases communicate between themselves you can move the logic of the communication to the programming layer. For example using PDO and PHP you can connect to both databases, get the data, mix it and produce a result. You can create an abstraction layer of PHP classes that get information independently from A or B databases, and later you will not care anymore about it, as you will work with PHP objects not directly with databases.
I've been asked to build a module for a web application, which will also be used as a stand alone website. Since this is the case, I wanted to use a separate database, and wondered if there was a way of having a table in one database, be a "pointer" in another database.
For example, I have databases db1 and db2
db1 has table users, so I want to have db2.users point to db1.users.
I know I could setup triggers and what not to sync two seperate tables but this sounds cooler :)
EDIT
So in my code I'm using sql such as
select * from users
Now, at the database level, I want "users" to actually be db1.users. Then, if I want to, I can remove the alias/pointer and "select * from users" will point to the users table in the current database. I guess what I'm looking for is a "global alias" type of thing.
Just use it directly from another database?
SELECT ... FROM `db1`.`users` LEFT JOIN `db2`.`something`
The federated storage engine offers something similar to the feature you asked for.
And if your databases are on the same database server, the federated storage enging sounds a bit like an overkill to me. You may want to create a view instead.
Both methods won't be useful if db1 is not available. As Emmerman already points out, you need to store the data in db2 if you want to prepare for the case of db1 being unavailable.
I used to use mysql, and in mysql database hold tables, but these concepts doesn't apply to oracle, so I don't quite understand the differences.
Update: The problem I am facing is, I need to do migration from Mysql to Oracle.
I have two switching databases called A and B, in Mysql all the tables are in their corresponding databases.
In mysql database is a logical concept, it use database to hold tables, in oracle database is physical concept, I don't know how to design this in oracle.
Do I need to use "CREATE DATABASE" to create two databases in oracle to achieve the same effect?
To answer your question you want to create a schema (CREATE USER) not an instance/database (CREATE DATABASE).
The Oracle definition of a database is the files on disk. These can be shared between instances (Real Application Clusters) or only used by a single instance (on the same server for example, the most common).
Background: The concept of "database" is different between database vendors. As an Oracle DBA I'm careful when talking to someone who is from an MySQL, DB2, SQL Server background, what they call a "database" in Oracle is a user/schema (difference between user and schema being a schema contains tables and a user is only a login). Whenever someone, developer especially, uses the word "database" question in what context.
Oracle's SQL Developer documentation has a chapter comparing MySQL with Oracle. Find it here. The reason it is here is because SQL Dev includes the Migration Workbench which supports migrating MySQL to Oracle. You might want to consider using the tool in your endeavours. It is free.
Anyway, the documentation has this answer to your specific question:
"When migrating MySQL databases to
Oracle, SQL Developer maps each MySQL
database to a tablespace in Oracle.
Database objects, such as tables,
indexes and views are stored in the
respective tablespaces and are
referenced from the Oracle schema for
the user that owns them."