1. Mastering Basic SQL: Your First Steps to Data Retrieval

SQL (Structured Query Language) is the indispensable tool for anyone working with data. At its heart, SQL is a language for talking to databases, and the foundation of that conversation lies in the basic structure of the SELECT statement.

To get started, let's use a simple sales database with three tables: Customer, Product, and Sales.

Table	Purpose
Customer	Holds customer details (CustomerID, Name, City)
Product	Holds product details (ProductID, Name, Price)
Sales	Holds transaction details (SaleID, CustomerID, ProductID, Date, Quantity)

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1. The Core: SELECT and FROM

The SELECT statement is how you tell the database exactly what data you want to see, and FROM tells it which table the data should come from.

• To retrieve all columns (use the asterisk *):

SELECT * FROM Product;

• To retrieve specific columns:

SELECT ProductID, Name FROM Product;

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2. Filtering Rows: The WHERE Clause

The WHERE clause is your primary tool for filtering data. It restricts the rows returned based on a specified condition.

• Retrieve all products priced over $50.00:

  
  SELECT * FROM Product WHERE Price > 50.00;

  
  

• Retrieve sales records made after a specific date:

  
  SELECT * FROM Sales where Date > '2024-01-01';

  
  

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3. Sorting Results: The ORDER BY Clause

The ORDER BY clause is used to sort the result set by one or more columns. Sorting helps you find minimums, maximums, or follow a chronological sequence.

• Sort products from highest price to lowest:

  
  SELECT * FROM Product ORDER BY Price DESC;

  
  

• Sort customer names alphabetically by City, and then by Name:

  
  SELECT * FROM customer ORDER BY City ASC, Name ASC;

  
  

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4. Limiting Results: The LIMIT Clause

The LIMIT clause (common in MySQL and PostgreSQL) is used to restrict the number of rows returned. This is essential for quickly checking the data or finding top records.

• Find the 5 most expensive products:

  
  SELECT * FROM Product ORDER BY Price DESC LIMIT 5;

  
  

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