Tutorials
Databases

The central concept of a database is that of a collection of records, or pieces of knowledge. Typically, for a given database, there is a structural description of the type of facts held in that database: this description is known as a schema. The schema describes the objects that are represented in the database, and the relationships among them.

Primary Key:
This is an index that cannot be NULL, Primary Keys are used in building relationships between tables in a database. (an index is automatically created on the primary key). The difference between primary and ordinary keys is that there can be multiple keys, but only one primary key.

Unique Key:
Unique and Index are same, the difference is, in Unique, duplicate are not allowed in any circumstances and that is enforced by database server.

Database tutorial for Data Warehouse

Data Mining is the process of extracting knowledge hidden from large volumes of raw data.

Before Designing Database for Data warehouse you should know-

 

  • What is a Data Warehouse? What is a Data Mart?
     
  • What is a Star Schema Database?
     
  • Why do I want/need a Star Schema Database?
     
  • The Star Schema looks very denormalized. Won’t I get in trouble for that?

     

    Reasons for Dirty Data

    Dummy Values
    Absence of Data
    Multipurpose Fields
    Cryptic Data
    Contradicting Data
    Inappropriate Use of Address Lines
    Violation of Business Rules
    Reused Primary Keys,
    Non-Unique Identifiers
    Data Integration Problems
     

    Biggest databases

    Company Database size (GB) DBMS
    France Telecom 29232 Oracle
    AT&T 26269 Daytona
    SBC 24805 Teradata
    • Databases
    Normilazation Rules
    Database deadlock
    SQL Tuning
    MySQL
    Databases Indexing
    Database indexing