SQL

This notebook is an exercise in the SQL course. You can reference the tutorial at this link. Introduction 介绍 Stack Overflow is a widely beloved question and answer site for technical questions. You’ll probably use it yourself as you keep using SQL (or any programming language). Stack Overflow 是一个广受欢迎的技术问题问答网站。 当您继续使用 SQL（或任何编程语言）时，您可能会使用它。 Their data is publicly […]

Introduction 介绍 You have the tools to obtain data from a single table in whatever format you want it. But what if the data you want is spread across multiple tables? 您可以使用工具以您想要的任何格式从单个表中获取数据。 但是，如果您想要的数据分布在多个表中怎么办？ That’s where JOIN comes in! JOIN is incredibly important in practical SQL workflows. So let’s get started. 这就是 JOIN 发挥作用的地方！ JOIN 在实际 […]

This notebook is an exercise in the SQL course. You can reference the tutorial at this link. import pandas as pd Introduction 介绍 You are getting to the point where you can own an analysis from beginning to end. So you’ll do more data exploration in this exercise than you’ve done before. Before you get […]

Introduction 介绍 With all that you’ve learned, your SQL queries are getting pretty long, which can make them hard understand (and debug). 根据您所学的知识，您的 SQL 查询变得相当长，这可能使它们难以理解（和调试）。 You are about to learn how to use AS and WITH to tidy up your queries and make them easier to read. 您将学习如何使用 AS 和 WITH 来整理您的查询并使它们更易于阅读。 Along the way, […]

This notebook is an exercise in the SQL course. You can reference the tutorial at this link. Introduction 介绍 You’ve built up your SQL skills enough that the remaining hands-on exercises will use different datasets than you see in the explanations. If you need to get to know a new dataset, you can run a […]

Introduction 介绍 So far, you’ve learned how to use several SQL clauses. For instance, you know how to use SELECT to pull specific columns from a table, along with WHERE to pull rows that meet specified criteria. You also know how to use aggregate functions like COUNT(), along with GROUP BY to treat multiple rows […]

This notebook is an exercise in the SQL course. You can reference the tutorial at this link. Introduction 介绍 Queries with GROUP BY can be powerful. There are many small things that can trip you up (like the order of the clauses), but it will start to feel natural once you’ve done it a few […]

Introduction 介绍 Now that you can select raw data, you’re ready to learn how to group your data and count things within those groups. This can help you answer questions like: 现在您可以选择原始数据，您已经准备好学习如何对数据进行分组并对这些组中的内容进行计数。 这可以帮助您回答以下问题： How many of each kind of fruit has our store sold? 我们店每种水果销售了多少？ How many species of animal has the vet office treated? […]

This notebook is an exercise in the SQL course. You can reference the tutorial at this link. Introduction 介绍 Try writing some SELECT statements of your own to explore a large dataset of air pollution measurements. 尝试编写一些自己的 SELECT 语句来探索空气污染测量的大型数据集。 Run the cell below to set up the feedback system. 运行下面的单元格来设置反馈系统。 # Set up feedback system […]

Introduction 介绍 Now that you know how to access and examine a dataset, you’re ready to write your first SQL query! As you’ll soon see, SQL queries will help you sort through a massive dataset, to retrieve only the information that you need. 现在您已经知道如何访问和检查数据集，您就可以编写您的第一个 SQL 查询了！ 您很快就会看到，SQL 查询将帮助您对海量数据集进行排序，以仅检索您需要的信息。 We’ll begin by using the keywords SELECT, […]