SQL Documentation

This guide introduces SQL (Structured Query Language) fundamentals, focusing on concepts and best practices for developers using the Codeunia Learn platform.

Overview

SQL is a standard language for managing relational databases. It handles data definition, manipulation, and querying. SQL is essential for data storage, retrieval, and analysis in applications.

SQL Fundamentals

Databases and Tables

Databases contain tables with rows and columns. Tables have schemas defining data types.

Data Types

Common types: INT, VARCHAR, TEXT, DATE, BOOLEAN, DECIMAL.

Primary Keys and Foreign Keys

Primary keys uniquely identify rows. Foreign keys link tables.

Data Definition Language (DDL)

Commands like CREATE, ALTER, DROP manage database structure.

Data Manipulation Language (DML)

INSERT, UPDATE, DELETE modify data.

Data Query Language (DQL)

SELECT retrieves data with clauses like WHERE, JOIN, GROUP BY, ORDER BY.

Joins

Inner, left, right, full joins combine data from multiple tables.

Aggregations

Functions like COUNT, SUM, AVG, MIN, MAX summarize data.

Subqueries

Nested queries for complex operations.

Indexes

Improve query performance by indexing columns.

Transactions

ACID properties ensure data integrity with COMMIT and ROLLBACK.

Views

Virtual tables created from queries.

Stored Procedures

Precompiled SQL code for reuse.

Best Practices

Normalize databases, use prepared statements, and optimize queries.

Popular Databases

MySQL, PostgreSQL, SQLite, SQL Server.

Resources and References

• SQLZoo
• W3Schools SQL
• PostgreSQL Documentation

Troubleshooting

Common issues include slow queries, data inconsistencies, and syntax errors. Use EXPLAIN for analysis.

Development Setup

Install a database server, use GUI tools like pgAdmin, and integrate with applications.