- A collection of data
- A method for accessing and manipulating that data
A major part of a data scientist's role involves handling data from a varity of data sources.
- Extraction the data out of production schema.
- Querying databse and concatenating datasets together.
- Cleaning and formatting data.
- Storing data into a suitable physical location so you can run your analysis.
Database Management System(DBMS) is a software for storing and retriving users data by considering appopriate security measures.It allows to create their own databases as per their requirement.
- -- A group od progra, which manipullate the database
- -- Provides an interface between databses and users
- -- Include details about the users of the databse and other application programs.
- -- Accept requests for data from an applicatiob and retrives the Specific data.
- -- Allows third-party software to store and retrive data.
| Hirarchial DBMS | Network DBMS | Object Oriented DBMS | RDBMS |
|---|
- -- An RDBMS is a subset of DBMS designed speecifically for relational databases.
- -- Is "relational" because the values within each table releated to each other.
- -- Table may also be related to each other.
- -- The relational structure make it possible to run queres across multiple tables.
| MySQL| Microsoft Access | Oracle | PostgreSQL | dBASE | FoxPro | SQLite | IBM DB2 | LibreOffice Base | MariaDB | Microsoft SQL Server |
-- The key attribute should never be NULL or same for two different rows of data.
-- Refers to the values that can be stored for a certain attibute.
- -- Referential integrity Constraints
- -- Referential integrity (RI) is a relational databse concept, which states that tabel relationship must always be consistent.(any foreign key field must agree with the primary key that refersed by the foreign key)
- -- If a table has a reference to some data from another table, then that data should be present for referential integrity constraint to hold true.
- --PRIMARY KEY : is the unique value key
- --Foreign key : Refrence to another table within a given table
-- NoSQL or most commonly know as 'Not only SQL' databse, it provides a mechanism for storage and retrival of unstructured data. It can handle a humongous amount of data and has dynamic schema. -- A NoSQL databse has no specific query language and no or very few relationship. Data is stored in the form of collections and documents.
| Types | KEY-VALUES STORIES | WIDE COLUMN STORES | DOCUMENT DATABASES | GRAPH DATABASES |
|---|---|---|---|---|
| Ex. | Redis, Riak,Voldemort | Cassandra,HBase | MongoDB | Neo4J, HyperGgaphDB |
| SQL | NoSQL |
|---|---|
| Relational database | Non-Relational database |
| Predifine schema | Dynamic schema |
| Table based databases | Key-value pair,documents, graph bases |
| Better fit for complex query enviroment | Not a good fit for complex queries |
| Vertically scalable | Horizontally scalable |
| Hevy-duty transactions | Not stable in high load and complex transactions |
| MySQL, Oracle,PostGreSQL | MongoDB ,Cassandra, HBase |
| DDL(Data Definition Language) | DML(Data Manipulation language) | DQL(Data Query Language) | DCL(Data Control Language) | TCL(Transaction Control Language) |
|---|---|---|---|---|
| DROP, RENAME,CREATE,ALTER,TRUNCATE | INSERT,UPDATE,DELETE | SELECT | GRANT,REVOKE | COMMIT,ROLLBACK,SAVEPOINT,SET,TRANSACTION |
Any object in a database that is used to store reference data. database objects are created using the create command They are used to hold and manipulate the data.
- -- Table : Basic unit of storage , Composed of rows and columns
- -- View : Logically represents subsets of data from one or more tables.
- -- Sequence : Generates primary key values
- -- Index : Improves the preformance of some queries
- Numeric Data Types
- Date and Time
- Large Object Data(LOB) Types