We can define a database link to be a connection between 2 databases or two or more physical databases. Database links plays an significant role in case of distributed databases. Link is a pointer which points towards another database or a server.
A Database link connection allows users to access data on a remote database. We can access the data from another database which is far away from our database with the help of database links.
Types of Database links :
We can classify our database links in 2 categories based on the rights assigned to access it.
1. Public links
2. Private links
In public databases links, everyone has right to access the database, view it or modify it from a location far away from the database on which we are working currently. In private database links, the one who created the database can view it, modify it or change it. It can be accessed by only those who created the database. It belongs to a particular schema and can be accessed by a particular group.
Types of links Links : 1. Connected user link 2. Fixed user link 3. Current user link
1.Connected User Link :
In this type, user connects as themselves, the user must have an account on the remote database having the same username and password as it was on the local database. In connected database user must have account on the remote database. We connect by using an database application.
2.Fixed User Link :
In case of fixed user database link, the local server builds a connection with a schema in the remote database. User connects through username and password along with the reference. For Example: if ABC uses a fixed user link that connects to the XYZ database with the username and password of Scott, then he/she connects as Scott, ABC has all the privileges in XYZ granted to Scott directly, and all the default roles that Scott has been granted in the XYZ database.
3.Current User Link :
In this case, user connects as a global user. When procedure, view, or trigger is executing, it initiates a database link. Here the current user is the name is not the user having the object but it is the user who has stored object. For Example: ABC can access a procedure that Scott wrote, accessing Scott’s account and Scott’s schema on the XYZ database.
Use of Database link:
Biggest benefit of database links is that it makes our work more easier and it allows user to access another user object at remote database. The great advantage of the database link is that they allow users to access another users object in a remote database. In other words we can say that a we can have a link to a remote database without having account on that database.
