A database is an organized collection of data. It is the collection of schemas, tables, views, and other objects. Databases support storage and manipulation of data. Databases make data management easy.
Database management system (DBMS) :
Database management system (DBMS) consisting of an integrated set of computer software that allows users to interact with one or more databases and provides access to all of the data contained in the database. The DBMS provides various functions that allow entry, storage and retrieval of large quantities of information and provides ways to manage how that information is organized.
Relational Database Management System :
A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as invented by E. F. Codd, of IBM’s San Jose Research Laboratory. In 2017, many of the databases in widespread use are based on the relational database model. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
Three keys terms are used extensively in Relational database model, those are relations, attributes and domains.
Relation : A relation is a table with columns and rows.
Attribute : A database attribute is a column name in a table in a database.
Domain : Domain is the set of values in an attribute which are allowed to take. For example, We can define Age(1-99) attribute in a table. The valid values are 1 to 99 only and the set of values called domain.
Table : The basic data structure of the Relational model is the table, where the information is stored within a database. It consists of columns, and rows.
Record or row : A row is a horizontal entity in a table. A row also called a record or tuple. Each row in a table represents a set of related data, and every row in the table has the same structure.
Column : A column is an vertical entity in a table that contains all information associated with a specific field in a table.
|Column 1||Column 2||Column 3|
|Row 1, Column 1||Row 1, Column 2||Row 1, Column 3|
|Row 2, Column 1||Row 2, Column 2||Row 2, Column 3|
|Row 3, Column 1||Row 3, Column 2||Row 3, Column 3|
Field : A field is an area in a unit of data such as a record. A field is the intersection of a row and a column i.e. if your table has 3 rows and 3 columns, it has 9 fields.
|Column 1||Column 2||Column 3|
|Row 1, Column 1, field 1||Row 1, Column 2, field 2||Row 1, Column 3, field 3|
|Row 2, Column 1, field 4||Row 2, Column 2, field 5||Row 2, Column 3, field 6|
|Row 3, Column 1, field 7||Row 3, Column 2, field 8||Row 3, Column 3, field 9|
The database schema, a set of related tables and other database objects and associated with one particular database username. It is a fundamental concept in relational databases and it is the logical database structure of any database.
Database administrator created username “testuser” and password for you. After log on create a table called EMP_INFO. According to the database, your table name is testuser.EMP_INFO. Here testuser is the schema name that you own.
As a owner you can query the table with or without schema name. But if any other user say user02 query the table, he should specify the schema name as testuser.EMP_INFO, with out schema name the table can’t find out.
Types of Relationships
- One to many
- One to One
- Many to Many
- First Normal Form 1NF
- Second Normal Form 2NF
- Third Normal Form 3NF
- Boyce-Codd Normal Form BCNF
- Fourth Normal Form 4NF
- Fifth Normal Form 5NF