On Day 4 of A2Z Challenge 2019, I shall talk about the A2Z of DBMS (Database Management System). A database is an organized collection of data, generally stored and accessed electronically from a computer system. DBMS is the software that interacts with the end user to read, write and update the database contents. In simple terms, DBMS acts as an intermediary between the end user and the database. The main objective of DBMS is to reduce Data redundancy and to main consistency.
A DBMS provides three different views of the database contents:
- External view: View of the data used by the end-users.
- Conceptual view: This view shows how tables are connected with each other. This is useful for database designers.
- Internal view: This view deals with the storage of the data in physical devices. This is generally used by Database Administrators.
A2Z of DBMS – Database Languages
One can read, update and store data in a database with the help of Database languages. They are DDL (Data Definition Language), DCL (Data Control Language), DML (Data Manipulation Language) and TCL (Transaction Control Language). SQL (Structured Query Language) combines the all 4 in a single language. SQL became the standard of the ANSI (American National Standards Institute) and ISO (International Organization for Standardization) in 1986 and 1987 respectively.
- DDL (Data Definiton Language): DDL is used to create database, tables, indexes etc. Some DDL statements include:
- CREATE: Create new database, table, index, view etc.
- ALTER: Modifies an existing database object.
- DROP: Destroys the database, table, index, view etc.
- RENAME: Set a new name for the table
- DML (Data Manipulation Language): DML is used for accessing and manipulating data in a database. Some DML statements include:
- SELECT: Fetches data from one or more tables in a database.
- INSERT: Adds one or more data to any single table in a database.
- UPDATE: Changes the data of one or more records in a table.
- DELETE: Removes one or more records from a table in a database.
- DCL (Data Control Language): DCL is used for granting and revoking user access on a database. DCL statements:
- GRANT: It is used to give user access privileges to a database.
- REVOKE: It is used to take back permissions from the user.
- TCL (Transaction Control Language): TCL is used to manage transactions in a database. TCL statements include:
- COMMIT: It is used to save the transaction on the database.
- ROLLBACK: It is used to restore the database to original since the last Commit.
In this article, I have touched the A2Z of DBMS in brief. If you have any questions, please ask them in the comments section.