Here is a complex sub-query on how to write it using two tables explained. One is the customer table, and the other one is the order table.
Sub-queries are two types. Single row return and Multiple-row return. Below is the multiple-row return example that explains in detail.
A subquery should get everything from the Customer_Table if the customer has an order in the Order_Table of greater than $400.
Here is Sub-query
select * from customer_table where customer_number in (select customer_number from order_table where order_total > 400);
How it works
The sub-query is inside the parenthesis. First, it gets the customer_number from the order_table (the order_total greater than 400).
The outer query gets all the details of customer_table for all the matching customer numbers.
I chose to use sub-query, which ultimately reduced complexity, and we got the desired result.
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