update database

data/database.md

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 ## Database Learning
 
+## Different type of database
+There are different type of database structures:
+1. Hierarchical database:
+   Follow a ranking order or parent-child relationship to structure data.
+
+2. Network database:
+   It's similar to Hierarchical database. but it connects the child record with various parent records and allowing two-directional relationships.
+
+3. Object-Oriented database:
+   System stores information of this type of database is an object-like manner.
+
+4. Relational database:
+   It's table-oriented, where every bit of data is linked to every other bit of data.
+
+5. Non-relational or NoSQL database:
+   There are varity of format support in No-SQL database, such as documents, graphs, wide columns, etc., which offers excellent flexibility and scalability to a database design.
+
+## Types of SQL Commands:
+- DDL – Data Definition Language <br>
+- DQL – Data Query Language
+- DML – Data Manipulation Language
+- DCL – Data Control Language
+- TCL – Transaction Control Language
+
+
+https://www.astera.com/type/blog/a-quick-overview-of-different-types-of-databases/
+
+### DDL (Data Definition Language):
+Set of SQL commands use to create, update and delete database structures but not data. <br>
+
+List of DDL Commands:<br>
+    1. Create: Used to create database or it's object<br>
+        (Like: Table, View, index, function, procedure & triggers)<br>
+    2. DROP: Used to delete database or it's object<br>
+    3. ALTER: Used to alter the database<br>
+    4. TRUNCATE: Used to delete all rows or remove all records from database table.<br>
+    5. COMMENT: Used to add comments to the data dictionary<br>
+    6. RENAME: Used to rename database objects.<br>
+
+
+### DQL (Data Query Language):
+This SQL commands allows to getting data out of the database to perform operations with it, used to show data imposing some order or grouping.<br>
+
+List of DQL Commands:<br>
+    1. SELECT: Used to retrive data from database<br>
+        (We may retrive data with or with out condition and grouping, may renderding data with some orders)<br>
+
+### DML (Data Manipulation Language):
+Set of SQL commands deal with data manipulation into database table.<br>
+
+List of DML Commands:<br>
+    1. INSERT: Used to insert/add data into table<br>
+    2. UPDATE: Used to updata existing data/rows into table with some condition<br>
+    3. DELETE: Used to delete existing data/row in table with some condition<br>
+    4. LOCK: Table control concurrency<br>
+    5. CALL: Call a PL/pgSQL or JAVA Subprogram<br>
+    6. EXPLAIN PLAN: Describe access path to data<br>
+
+### DCL (Data Control Language):
+This type of SQL commands used to give rights, permissions and other controls of the database system.<br>
+
+List of DCL commands:<br>
+    1. GRANT: Give users access privileges to db<br>
+    2. REVOKE: Withdraws the users access privileges given by using the GRANT command.<br>
+
+### TCL (Rransaction Control language):
+Transaction group is a set of tasks in a single execution unit. Each transaction begins with a specific task and ends when all the taks in the group are succesfully completed.<br> 
+If any task fail, then whole transaction is failed. <br>
+Therefore, every transaction has only two results: 'Success' or 'Failure'.<br>
+
+List of TCL commands:<br>
+    1. BEGIN: Opens a Transaction<br>
+    2. COMMIT: Commits a Transaction<br>
+    3. ROLLBACK: Rollbacks a transaction in case of any error occurs.<br>
+    4. SAVEPOINT: Sets a save point within a transaction<br>
+
+
+
+
+Refference:<br>
+    1. [astera.com](https://www.astera.com/type/blog/a-quick-overview-of-different-types-of-databases/)<br>
+    2. [GeeksforGeeks](https://www.geeksforgeeks.org/sql-ddl-dql-dml-dcl-tcl-commands/)<br>
+    3. [javatpoint](https://www.javatpoint.com/dbms-sql-command)<br>
+    4. 
 
-DDL – Data Definition Language
-DQL – Data Query Language
-DML – Data Manipulation Language
-DCL – Data Control Language
-TCL – Transaction Control Language
 
 
-https://www.astera.com/type/blog/a-quick-overview-of-different-types-of-databases/