SQL Full Overview

Table of Contents

1. Introduction to SQL
2. SQL Language Structure
3. Basic SQL Commands
4. Data Manipulation Commands
5. Data Definition Commands
6. Data Control Commands
7. Advanced SQL Topics
8. SQL Best Practices
9. Common SQL Databases
10. Conclusion

Introduction to SQL

SQL (Structured Query Language) is a programming language designed for managing and manipulating data stored in relational database management systems (RDBMS). SQL is used to perform various operations such as creating, modifying, and querying databases.

Key Features of SQL:

• Declarative Language: You specify what you want to do, not how to do it.
• Standardized: SQL is standardized by ANSI, but different databases may have variations.
• Query Language: SQL is primarily used for querying data.
• Programming Language: SQL can also be used to create and modify database structures.

Common SQL Databases

There are many SQL databases available, each with their own strengths and weaknesses. Some of the most popular ones include:

• MySQL: Open-source, widely used for web applications.
• MariaDB: A fork of MySQL, also open-source.
• PostgreSQL: Open-source, known for its advanced features and reliability.
• Microsoft SQL Server: Proprietary, widely used in enterprise environments.
• Oracle: Proprietary, known for its scalability and enterprise features.

SQL Language Structure

SQL syntax is composed of several elements including keywords, identifiers, literals, and symbols. Here are some basic elements:

Keywords

These are reserved words that have special meaning in SQL. Examples include:

• SELECT
• FROM
• WHERE
• CREATE
• DROP

Identifiers

These are names given to databases, tables, columns, etc. They must follow certain rules, such as not being a reserved keyword and starting with a letter or underscore.

Literals

These are actual values used in SQL statements. Examples include:

• 1 (numeric literal)
• 'Hello World' (string literal)
• '2023-10-01' (date literal)

Symbols

SQL uses various symbols such as:

• * : Wildcard character to select all columns.
• ; : Statement terminator.
• () : Used to group expressions and define function parameters.
• "" or '' : Used to enclose string literals.

Basic SQL Commands

Here are some basic SQL commands that you should know:

SELECT Statement

The SELECT statement is used to retrieve data from one or more tables.

SELECT column1, column2, ...
FROM tablename;

Example:

SELECT employee_id, first_name, last_name
FROM employees
WHERE department = 'Sales';

SELECT Clauses

• SELECT: Specifies the columns to retrieve.
• FROM: Specifies the table(s) to retrieve data from.
• WHERE: Filters records based on conditions.
• AND, OR, NOT: Used to combine conditions.
• ORDER BY: Sorts the result set in ascending or descending order.
• LIMIT: Limits the number of rows returned.
• DISTINCT: Returns only distinct values.

Wildcards

The * wildcard is used to select all columns.

SELECT *
FROM employees
WHERE salary > 50000;

INSERT Statement

The INSERT statement is used to add new records to a database table.

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

Example:

INSERT INTO employees (employee_id, first_name, last_name, department)
VALUES (101, 'John', 'Doe', 'Sales');

UPDATE Statement

The UPDATE statement is used to modify existing records in a database table.

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

Example:

UPDATE employees
SET department = 'Marketing', salary = 60000
WHERE employee_id = 101;

DELETE Statement

The DELETE statement is used to delete records from a database table.

DELETE FROM table_name
WHERE condition;

Example:

DELETE FROM employees
WHERE employee_id = 101;

Data Manipulation Commands

Data manipulation commands are used to modify and manage data in a database.

INSERT

Used to add new records.

INSERT INTO customers (customer_id, name, email)
VALUES (1, 'John Doe', '[email protected]');

UPDATE

Used to modify existing records.

UPDATE customers
SET email = '[email protected]'