Difference between RDBMS and DBMS:

Usually in file processing system, records are stored permenently in various files. A number of application programs are written to extract records from, add records to and update records in the files. This style of file processing may lead to some drawbacks such as data redundancy (duplication of data), data inconsistency, non-sharable of data, non-standardized data, insecure data, incorrect data, invalid data etc. To overcome all these problems the software called database management system (DBMS) is used, which provides a centralized control of the data. The overall DBMS consists of databases, database languages, and the users.

DBMS

DataBase Management System (DBMS) is defined as the software program that is used to manage all the databases that are stored on the network or system hard disk. There are different types of database management systems and some of them are configured for specific purposes.

DBMS is available in different forms as a tool that is used to manage databases. Some popular DBMS solutions include DB2, Oracle, FileMaker and Microsoft Access. Using these products, privileges or rights can be created that can be specific to particular users. It means that the administrators of the database can grant specific rights to some users or assign different levels of administration.

Every DBMS has some fundamental elements. First is the implementation of the modeling language which defines the language used for each database. Second, DBMS also administers the data structures. Data query language is the third element of a DBMS. Data structures work with data query language in order to make sure that irrelevant data cannot be entered into the database used in the system.

RDBMS

In 1970s, Edgar Frank Codd introduced the theory of relational database. Thirteen rules were defined by Codd for this relational theory or model. Relationships among different types of data Is the main requirement of the relational model.

The database system in which the relationships among different tables are maintained is called Relational Database Management System. Both RDBMS and DBMS are used to store information in physical database. Whereas RDBMS solution is required when large amounts of data are to be stored as well as maintained.

A relational data model consists of indexes, keys, foreign keys, tables and their relationships with other tables. Relational DBMS enforces the rules even though foreign keys are support by both RDBMS and DBMS.

Difference between DBMS & RDBMS

• Database management (DBMS) is considered as the system to store the data for easy retieval and the data were relatively stored as a group. Whereas, Relational database management system (RDBMS) will include a relationship between tables (using constraints). The relationship will be based on their logical relations.
• DBMS accepts the ‘flat file’ data that means there is no relation among different data whereas RDBMS does not accepts this type of design.
• DBMS is used for simpler business applications and small sets of data whereas RDBMS is used for more complex applications and large sets of data.
• Although the foreign key concept is supported by both DBMS and RDBMS but its only RDBMS that enforces the rules.

Let us consider that there are two table "employee" which will hold employee information like, employee id, employee dob, where he is working. Another table "employee details" which may hold his personal information like blood group, identification etc.., For these two tables, there should be a key which will form a relation ship between these two tables. Its nothing but RDBMS. (Eg: SQL Server, Oracle)

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Sub Query

• Sub-queries are often referred to as sub-selects, as they allow a SELECT statement to be executed arbitrarily within the body of another SQL statement.
  
• Sub-queries are generally used to return a single row as an atomic value, though they may be used to compare values against multiple rows with the IN keyword.
  
• A sub query SELECT statement can return any number of values, and can be found in, the column list of a SELECT statement, a FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement.
  

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Types of sub-queries

• Single-row sub query, where the sub query returns only one row.
  
• Multiple-row sub query, where the sub query returns multiple rows.
  
• Multiple column sub query, where the sub query returns multiple columns
  

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Cursor

• Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.
  
• In order to work with a cursor we need to perform some steps in the following order:
  
  • Declare cursor
    
  • Open cursor
    
  • Fetch row from the cursor
    
  • Process fetched row
    
  • Close cursor
    
  • De allocate cursor
    

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