What is DBMS ?

 ### DBMS (Database Management System)


A **Database Management System (DBMS)** is software that interacts with the user, applications, and the database itself to capture and analyze data. A DBMS allows users to create, read, update, and delete data in a database. It ensures data integrity, security, and concurrency while providing support for data manipulation and retrieval.


#### Types of DBMS


1. **Hierarchical DBMS**:

   - Data is organized in a tree-like structure.

   - Example: IBM Information Management System (IMS).


2. **Network DBMS**:

   - Data is organized in a graph, allowing many-to-many relationships.

   - Example: Integrated Data Store (IDS).


3. **Relational DBMS (RDBMS)**:

   - Data is stored in tables (relations) and can be linked based on data common to each.

   - Examples: MySQL, PostgreSQL, Oracle, Microsoft SQL Server.


4. **Object-oriented DBMS (OODBMS)**:

   - Data is stored in objects, similar to object-oriented programming.

   - Example: db4o, ObjectDB.


5. **NoSQL DBMS**:

   - Designed for unstructured data and provides a mechanism for storage and retrieval of data that is modeled in means other than tabular relations used in relational databases.

   - Examples: MongoDB, Cassandra, Redis.


### SQL (Structured Query Language)


**SQL** is a standard programming language specifically designed for managing and manipulating databases. SQL is used to perform various operations on the data within a relational database.


#### Basic SQL Commands


1. **Data Definition Language (DDL)**:

   - Commands that define the structure of the database.

   - Examples:

     - `CREATE TABLE`: Creates a new table.

     - `ALTER TABLE`: Modifies an existing table.

     - `DROP TABLE`: Deletes a table.


   ```sql

   CREATE TABLE employees (

       id INT PRIMARY KEY,

       name VARCHAR(100),

       position VARCHAR(100),

       salary DECIMAL(10, 2)

   );

   ```


2. **Data Manipulation Language (DML)**:

   - Commands that manipulate the data within the database.

   - Examples:

     - `INSERT INTO`: Adds new data into a table.

     - `UPDATE`: Modifies existing data within a table.

     - `DELETE`: Removes data from a table.

     - `SELECT`: Retrieves data from one or more tables.


   ```sql

   INSERT INTO employees (id, name, position, salary) VALUES (1, 'John Doe', 'Manager', 60000.00);

   ```


3. **Data Control Language (DCL)**:

   - Commands that control access to the data within the database.

   - Examples:

     - `GRANT`: Gives user's access privileges to the database.

     - `REVOKE`: Takes back permissions granted to the user.


   ```sql

   GRANT SELECT ON employees TO user_name;

   ```


4. **Transaction Control Language (TCL)**:

   - Commands that manage transactions within the database.

   - Examples:

     - `COMMIT`: Saves the transaction permanently in the database.

     - `ROLLBACK`: Restores the database to its last committed state.

     - `SAVEPOINT`: Sets a savepoint within a transaction to which one can rollback.


   ```sql

   BEGIN TRANSACTION;

   UPDATE employees SET salary = salary * 1.10 WHERE position = 'Manager';

   COMMIT;

   ```


#### Example Languages for DBMS


1. **SQL**:

   - Standard language for relational databases.

   - Examples: MySQL, PostgreSQL, Oracle SQL.


2. **PL/SQL** (Procedural Language/SQL):

   - Oracle Corporation's procedural extension for SQL.

   - Used in Oracle databases.


3. **T-SQL** (Transact-SQL):

   - Microsoft's and Sybase's proprietary extension to SQL.

   - Used in Microsoft SQL Server and Sybase ASE.


4. **MongoDB Query Language (MQL)**:

   - Used for querying MongoDB NoSQL databases.


5. **CQL (Cassandra Query Language)**:

   - Used for querying Apache Cassandra.


These languages and commands provide the means to create, modify, manage, and interact with databases effectively.

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