course_sql

SQL 1 - Introduction

Please install the SQLite DB Browser

A database is a structured collection of data organized in a way that allows for efficient storage, retrieval, and management. It is typically organized into tables, which consist of rows and columns, similar to a spreadsheet.
Databases help prevent anomalies and errors during data operations such as updates, inserts, or deletes by enforcing data integrity and relationships between data elements.
Example: A relational database might store customer information in one table and order information in another, linking them through a common key.

A DBMS is software that provides an interface for users to interact with databases, managing the storage, retrieval, and modification of data.
It ensures data integrity, security, and concurrency control, allowing multiple users to access the database simultaneously without conflicts.
Example: Popular DBMS include MySQL, PostgreSQL, and SQLite, each offering unique features and capabilities.

**Advantages:**
Centralizes data storage, making it easier to manage and access.
Ensures data integrity by enforcing data types and constraints.
Provides security features to protect sensitive data.
Allows for efficient data retrieval and manipulation, especially with large datasets.
Overcomes limitations of tools like Excel, which can handle only a limited number of rows.
**Disadvantages:**
High initial setup costs for hardware and software.
Requires skilled administrators to manage and maintain the system.
Less flexible than unstructured data storage methods, such as Excel files.

SQL is a programming language specifically designed for managing and manipulating relational databases.
It provides a standardized way to perform operations such as creating, modifying, and querying databases, making it essential for database management.
Common SQL operations include:
**SELECT**: Retrieve data from one or more tables.
**INSERT**: Add new records to a table.
**UPDATE**: Modify existing records in a table.
**DELETE**: Remove records from a table.

A database consists of multiple tables, each containing rows (records) and columns (fields).
**Record**: A horizontal row in a table representing a single entry.
**Field**: A single value in a record, similar to a cell in Excel, typically named in singular form.
**Primary Key**: A unique identifier for each record in a table, often an auto-incrementing integer, ensuring no null values.
**Foreign Key**: A field that creates a link between two tables, maintaining referential integrity by pointing to a primary key in another table.

**Integer**: Whole numbers (e.g., 1, 2, 3), often referred to as ‘int’.
**Float**: Non-whole numbers (e.g., 1.2, 2.8), sometimes called ‘double’ or ‘money’.
**String**: Text values (e.g., ‘Bob’, ‘Sarah’), often referred to as ‘VARCHAR’ for variable-length characters.

**Schema**: The data model that defines the structure of the database, including tables, fields, and relationships.
**Data Dictionary**: A comprehensive definition of the fields and tables in a database, serving as a reference for database design and usage.

A database diagram visually represents multiple tables and their relationships, providing a graphical view of the database structure.
Example: The Northwind SQL Diagram illustrates how various tables (e.g., Products, Suppliers) are interconnected, aiding in understanding data flow and relationships.

Recommended naming conventions include using lowercase letters, avoiding spaces, and utilizing underscores (e.g., product_id).
When dealing with columns that have spaces or special characters, wrap them in double quotes to ensure proper handling in SQL queries.

Northwind SQL Diagram