Introduction to RDBMS:-
- RDBMS stands for Relational Database Management System.
- RDBMS is based on relational model.
- Relational model invented by Dr. E. F. Codd in 1970.
- The relational model is an attempt to simplify the database structure.
- Relational model represents all data in database as simple tables in the row-column format.
I_CODE | NAME | AGE | SEMESTER |
11001 | NANCY MATHEW | 27 | I |
11002 | CATHERINE | 38 | II |
11003 | MAC | 50 | IV |
11004 | NELSON | 35 | III |
- RDBMS is can be defined as Database Management System (DBMS) where all data visible to the user is organized strictly as tables of data values, and where all database operations work on these tables.
- Examples of RDBMS : SQL, Sybase, Oracle, Microsoft SQL Server, Ingress, DB2, MySQL, PostgreSQL.
Relational Data Structure:-
- The organizing principle in a relational database is the table, a tabular arrangement of data values. Each table in a database has a unique table name that identifies its contents. A table is called a relation.
- The row (or record) in the table is called a tuple. The number of tuples is called the cardinality of the table. Let’s see a row or record in the table-
- The column (or field) is called an attribute. Every column in a table must have a unique name. The number of attributes is called the degree of the table. Let’s see a column or attribute in the table-
- Field is a smaller entity of the table which contains specific information about every record in the table. For example,
- One important property of a relation is that its rows are unordered. A row cannot be identified by its position in the table. Every table must have some columns or combination of columns that uniquely identifies each row in the table. At any given time, no two rows of the table contain the same values in that column or column combination. This column (or columns) is called primary key of the table.
For example, in the student table, ROLL_NO is the primary key as it uniquely identifies each student.
| 11001 | NANCY MATHEW | 27 | I |
| NANCY MATHEW |
| CATHERINE |
| MAC |
| NELSON |
| I_CODE | NAME | AGE | SEMESTER |
NULL Value :-
The SQL NULL is the term used to represent a missing value. A NULL value in a table is a value in a field that appears to be blank.
A field with a NULL value is a field with no value. NULL value is different than a zero value or a field that contains spaces.Data Integrity:-
Data integrity ensures the consistency and correctness of data stored in database.
Data Integrity is classified into the following four categories:
- Entity integrity: Entity integrity ensure that each row can be uniquely identified by an attribute called the primary key. The Primary Key cannot be NULL.
- Domain integrity : Domain integrity can be enforced by restricting the type of data, the range of values, and the format of the data.
- Referential integrity : Referential integrity ensures that the values of the foreign key match with the value of the corresponding primary key (i.e., rows cannot be deleted, which are used by other records).
- User-defined integrity : User-defined integrity refers to a set of rules specified by a user, which do not belong to the entity, domain, and referential integrity.
Applications of RDBMS:-
Some typical applications of an RDBMS are:- Airline and railway reservations
- Banking applications
- Manufacturing industry
- Order processing
- Hospital management system
- Library management system
- Hotel industry
