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Database languages

What is Database languages

Database languages are specialized programming languages used to interact with databases. They enable users to perform various operations such as querying, updating, inserting, and deleting data from databases. There are several types of database languages, each serving specific purposes:

Type Of Daabase Languages

  • Data Definition Language (DDL)
  • Data Manipulation Language (DML)
  • Data Control Language (DCL)
  • Transaction Control Language (TCL)
  • Query Languages
  • Programming Languages with Database Connectivity

Data Definition Language (DDL):

  • DDL is used to define the structure and organization of the database schema.
  • Common DDL commands include CREATE (to create database objects like tables, indexes, and views), ALTER (to modify the structure of existing database objects), and DROP (to delete database objects).
CREATE TABLE Employees (
    EmployeeID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    DepartmentID INT,
    Salary DECIMAL(10,2)
);

ALTER TABLE Employees
ADD COLUMN Email VARCHAR(100);

DROP TABLE Employees;

Data Manipulation Language (DML):

  • DML is used to manipulate data within the database. It includes commands for querying, inserting, updating, and deleting data.
  • The most common DML command is SQL (Structured Query Language), which is used in relational database management systems (RDBMS) like MySQL, Oracle, SQL Server, and PostgreSQL.
-- Inserting data
INSERT INTO Employees (EmployeeID, FirstName, LastName, DepartmentID, Salary)
VALUES (1, 'John', 'Doe', 101, 50000.00);

-- Updating data
UPDATE Employees
SET Salary = 55000.00
WHERE EmployeeID = 1;

-- Deleting data
DELETE FROM Employees
WHERE EmployeeID = 1;

Data Control Language (DCL):

  • DCL is used to control access to the database and its objects.
  • DCL commands include GRANT (to give users specific privileges on database objects) and REVOKE (to remove previously granted privileges).
-- Granting privileges
GRANT SELECT, INSERT, UPDATE, DELETE ON Employees TO HR_User;

-- Revoking privileges
REVOKE INSERT, UPDATE ON Employees FROM HR_User;

Transaction Control Language (TCL):

  • TCL is used to manage transactions within the database.
  • TCL commands include COMMIT (to save the changes made by a transaction), ROLLBACK (to undo the changes made by a transaction), and SAVEPOINT (to set a point within a transaction from which to roll back).
-- Starting a transaction
BEGIN TRANSACTION;

-- Making changes
INSERT INTO Employees (EmployeeID, FirstName, LastName, DepartmentID, Salary)
VALUES (2, 'Jane', 'Smith', 102, 60000.00);

-- Committing the transaction
COMMIT;

-- Rolling back changes
ROLLBACK;

Query Languages:

  • These languages are used specifically for querying databases to retrieve information.
  • SQL (Structured Query Language) is the most widely used query language, especially in relational database management systems (RDBMS).
  • Other query languages include:
    • Datalog: A declarative logic-based language used for querying and manipulating relational databases.
    • SPARQL: A query language used to retrieve and manipulate data stored in Resource Description Framework (RDF) format, commonly used in semantic web applications.
-- Basic SQL query
SELECT FirstName, LastName, Salary
FROM Employees
WHERE DepartmentID = 101;

Programming Languages with Database Connectivity:

  • These are general-purpose programming languages that provide libraries or APIs for interacting with databases.
  • Examples include:
    • JDBC (Java Database Connectivity) for Java
    • ADO.NET for .NET languages like C# and VB.NET
    • psycopg2 for Python interacting with PostgreSQL
    • mysqli for PHP interacting with MySQL

Example using Python and SQL:

import sqlite3

# Connect to the database
conn = sqlite3.connect('example.db')

# Create a cursor object
cursor = conn.cursor()

# Execute SQL query
cursor.execute('''
CREATE TABLE IF NOT EXISTS Employees (
    EmployeeID INT PRIMARY KEY,
    FirstName TEXT,
    LastName TEXT,
    DepartmentID INT,
    Salary REAL
)
''')

# Insert data
cursor.execute('''
INSERT INTO Employees (EmployeeID, FirstName, LastName, DepartmentID, Salary)
VALUES (?, ?, ?, ?, ?)
''', (1, 'John', 'Doe', 101, 50000.00))

# Commit changes
conn.commit()

# Close connection
conn.close()

    Each of these database languages serves a specific purpose in managing and interacting with databases, providing users with the flexibility and power to work with data effectively.

    These are some of the fundamental DDL commands used in SQL. They are essential for creating, modifying, and managing the structure of database objects, allowing users to define the organization and layout of their data within a database system.

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