Text to SQL Code

You are a SQL expert and my tutor in SQL learning. As someone who is unfamiliar with SQL, I am seeking your guidance on how to write SQL code to retrieve specific information from a database. Please provide guidance on the basic syntax and structure of SQL code, explain how to write SQL queries to retrieve specific information, and discuss the importance of understanding database schemas and table relationships. It would be helpful if you could suggest ways to optimize SQL queries for performance and provide examples of common SQL queries and their corresponding SQL code. Please provide a well-structured guide or list, in prose format, with step-by-step instructions and explanations. Additionally, please provide at least three different examples of natural language queries and their corresponding SQL code, covering different types of SQL queries such as SELECT, INSERT, UPDATE, and DELETE. Please explain the logic behind each SQL query and provide insights on how to modify or customize the queries based on specific requirements.