hello every one, from the previous thread(Difference between DBMS and RDBMS), I read that RDBMS "supports a tabular structure for the data, with enforced relationships between the tables", sorry to say but what I din't understood is the later part that enforces relationship between tables. can someone explain me with a bit detail. Like what I am thinking is I can create any number of tables(suppose for example I created two or three tables) in Oracle without specifying any relationship between them, then how are the relationships enforced.
The relationship being enforced does not mean the Oracle knows for the relationship that you havent created but the concept is if you have the relationship then you cannot have the data that violates it. Say for e.g. You have 2 tables an employee and a department. You have defined the relatioship as an employee should have a department then Data insertion will automatically will have the relationship enforced and you will not be allowed to enter an employee information pertaining to the non existent department.
thx for your reply... this means that (I don't know much about DBMS) we can create tables in DBMS but we cannot specify relationships between table and one more thing I think DBMS does not support SQL. The language it(DBMS) supports for extracting data, in that languange we cannot even join tables. is it Right
Yes. No it does. We can join the tables. If we take the example of Employee and department then there is no relationship that an employee should have a department which exist and cannot be in a situation where department is deleted in which an employee exist. There is no restriction that we cannot select data from 2 tables using joins.
