Welcome back to another insightful journey into the world of SQL. In today's lesson, we're diving deep into the realm of SQL Server Nested Queries. Buckle up as we explore how to execute nested queries and unravel the crucial 'why' behind their necessity. Let's get to work!
Click here for the GitHub link to the spreadsheet and SQL scripts for this lesson.
Understanding Nested Queries
Nested queries, essentially queries within queries, become indispensable when a single query falls short of providing the comprehensive data insights we need. Today, we'll navigate through a simple dataset comprising names, states, and sales.
Exploring Data Questions
Imagine facing data-related questions from business stakeholders or seeking insights for your own company. We'll address common queries: What's the average sale? What's the average sale by person? How about the average sale by state? And finally, what if we want the average of an average?
Step-by-Step Analysis
Breaking down the dataset into manageable chunks, we'll answer these questions step by step. The provided spreadsheet and SQL code will guide you through the process.
Average Sale: Simple query
select avg(sales) as average_sales from Sales
Average Sale by Name: Grouping by name
select Name, avg(sales) as average_sales from Sales group by name
Nested Query - Average of Averages (by Name): Nesting the previous query
select avg(average_sales) average_sales_by_name from (select Name, avg(sales) as average_sales from Sales group by name) avg_sales_by_name
Average Sale by State: Grouping by state
select State, avg(sales) as average_sales from Sales group by State
Nested Query - Average of Averages (by State): Nesting the state query
select avg(average_sales) average_sales_by_state from (select State, avg(sales) as average_sales from Sales group by State) avg_sales_by_state
Average Sales by Name, State: Grouping by name and state
select Name, State, avg(sales) as average_sales from Sales group by name, state
Nested Query - Average of Averages (by State and Name): Nesting the state query
select State, avg(average_sales) average_sales_by_name_state from (select Name, State, avg(sales) as average_sales from Sales group by name, state) avg_sales_by_name group by state
select avg(average_sales_by_name_state) from ( select State, avg(average_sales) average_sales_by_name_state from(select Name, State, avg(sales) as average_sales from Sales group by name, state) avg_sales_by_name group by state) average_name_state
Bonus Quick Tip
You can achieve similar results by creating and using a view of a view.
Mastering nested queries opens up a world of possibilities in SQL data analysis. Remember, it's all about breaking down complex questions into manageable parts. Don't forget to download the spreadsheet and SQL code to reinforce your learning. We hope you found this lesson helpful. Have a fantastic day!
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