Sorting and Limiting Results

In this lesson, you'll learn how to sort and limit the results of your SQL queries. This is crucial for organizing your data and focusing on the most relevant information. We'll explore the `ORDER BY` and `LIMIT` clauses and how they can be used to control the output of your queries.

Learning Objectives

  • Understand how to use the `ORDER BY` clause to sort query results.
  • Learn how to specify the sorting order (ascending or descending).
  • Master the use of the `LIMIT` clause to restrict the number of rows returned.
  • Combine `ORDER BY` and `LIMIT` to efficiently retrieve the most important data.

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Lesson Content

Introduction to Sorting with `ORDER BY`

When you retrieve data from a database, the order of the results is often arbitrary. The ORDER BY clause allows you to sort the results based on one or more columns. The general syntax is:

SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ...;

By default, the sorting is done in ascending order (A-Z, 0-9). Let's see an example. Suppose we have a products table with columns like product_id, product_name, and price. To sort products by price, we would use:

SELECT product_id, product_name, price
FROM products
ORDER BY price;

Specifying Sort Order (ASC and DESC)

You can explicitly specify the sort order using ASC (ascending) or DESC (descending). ASC is the default. To sort the products table in descending order of price, use:

SELECT product_id, product_name, price
FROM products
ORDER BY price DESC;

You can also sort by multiple columns. For example, to sort by price (descending) and then by product name (ascending) for products with the same price:

SELECT product_id, product_name, price
FROM products
ORDER BY price DESC, product_name ASC;

Limiting Results with `LIMIT`

The LIMIT clause restricts the number of rows returned by a query. This is incredibly useful for looking at the top few or bottom few results. The syntax is:

SELECT column1, column2, ...
FROM table_name
LIMIT number_of_rows;

For example, to find the 3 most expensive products:

SELECT product_id, product_name, price
FROM products
ORDER BY price DESC
LIMIT 3;

Note the order of the clauses: ORDER BY before LIMIT.

Combining `ORDER BY` and `LIMIT`

The power of ORDER BY and LIMIT is realized when used together. By sorting and limiting, you can extract the most important information from a large dataset. Let's say you want to see the 5 cheapest products:

SELECT product_id, product_name, price
FROM products
ORDER BY price ASC
LIMIT 5;

This query first sorts the products by price in ascending order (cheapest first) and then returns only the first 5 rows (the 5 cheapest products).

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