Introduction to SQL

SQL, or Structured Query Language, is a standard programming language specifically designed for managing and manipulating relational databases. SQL is used to perform tasks such as querying data, inserting new records, updating existing data, deleting records, and defining database structures.

Key Features of SQL

Declarative Language: SQL specifies what to do rather than how to do it.
Data Manipulation: It allows retrieving, inserting, updating, and deleting data from tables.
Data Definition: SQL includes commands to create, modify, and delete database structures like tables.
Data Control: SQL manages permissions and access to the database through Data Control Language (DCL).

Common SQL Commands

SQL commands can be categorized into five main types:

Data Query Language (DQL): Fetch data from the database.
- Example: SELECT
Data Definition Language (DDL): Define or modify database structures.
- Examples: CREATE, ALTER, DROP
Data Manipulation Language (DML): Modify data in the database.
- Examples: INSERT, UPDATE, DELETE
Data Control Language (DCL): Control access to data.
- Examples: GRANT, REVOKE
Transaction Control Language (TCL): Manage database transactions.
- Examples: COMMIT, ROLLBACK, SAVEPOINT

Basic SQL Syntax

Here is an overview of commonly used SQL commands with examples:

1. SELECT Statement

Used to retrieve data from a table.

  SELECT column1, column2
  FROM table_name
  WHERE condition;

Example: Retrieve all employees from the employees table who earn more than $50,000.

  SELECT first_name, last_name, salary
  FROM employees
  WHERE salary > 50000;

2. INSERT INTO Statement

Used to insert new rows into a table.

  INSERT INTO table_name (column1, column2, column3)
  VALUES (value1, value2, value3);

Example: Add a new employee to the employees table.

  INSERT INTO employees (first_name, last_name, job_title, salary)
  VALUES ('Jane', 'Doe', 'Software Engineer', 75000);

3. UPDATE Statement

Used to update existing records.

  UPDATE table_name
  SET column1 = value1, column2 = value2
  WHERE condition;

Example: Increase the salary of all employees in the IT department by 10%.

  UPDATE employees
  SET salary = salary * 1.10
  WHERE department = 'IT';

4. DELETE Statement

Used to delete records from a table.

  DELETE FROM table_name
  WHERE condition;

Example: Remove employees who are no longer active.

  DELETE FROM employees
  WHERE status = 'Inactive';

5. CREATE TABLE Statement

Used to create a new table.

  CREATE TABLE table_name (
      column1 datatype constraints,
      column2 datatype constraints,
      ...
  );

Example: Create a customers table.

  CREATE TABLE customers (
      customer_id INT PRIMARY KEY,
      first_name VARCHAR(50),
      last_name VARCHAR(50),
      email VARCHAR(100),
      phone_number VARCHAR(15)
  );

6. ALTER TABLE Statement

Used to modify the structure of an existing table.

  ALTER TABLE table_name
  ADD column_name datatype;

Example: Add a new column date_of_birth to the customers table.

  ALTER TABLE customers
  ADD date_of_birth DATE;

7. DROP TABLE Statement

Used to delete an entire table.

  DROP TABLE table_name;

Example: Remove the old_data table.

  DROP TABLE old_data;

Conclusion

SQL is a versatile and essential tool for database management. It is widely used across industries for tasks ranging from simple data retrieval to complex database operations. Mastering SQL involves understanding its syntax, practicing with examples, and applying it to real-world scenarios.

HTML

JAVASCRIPT

CSS

PYTHON

JAVA

SQL

Introduction to SQL