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Find customers with at least one order in each table
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SQL Problems
Given two tables, this SQL query finds all customers who have at least one order in each table.
Find the number of unique users in a table
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SQL Problems
The goal is to find the number of unique users in a table. The table has the following columns: user_id, name. The query should return the number of unique users. In the example above, the answer would be 3.
"Return the total value of all products in a database table"
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SQL Problems
Given a database table with a schema as shown above, write a SQL query that returns the total value of all products in the table.
Get names and total spending for customers who have made a purchase in the...
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SQL Problems
This technical problem asks the reader to write a SQL query that returns the names and total spending for customers who have made a purchase from the store in the last 30 days. The input is provided in the form of two tables, customers and orders, and the output is expected in the form of a table with two columns, name and total_spent.
Designing a Database Schema for a Library System
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SQL Problems
Design a database schema for a library system that keeps track of books, patrons, and checkouts. The system should allow patrons to check out multiple books at a time, and should keep track of when books are due back.
Find all pairs of rows with overlapping start and end times.
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SQL Problems
Given a table of data with three columns: id, start, and end, this SQL query will find all pairs of rows where the start and end times overlap.
Creating a Backup and Recovery Plan for a Database
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SQL Problems
You are tasked with creating a backup and recovery plan for a database. The database is currently running on a single server. The backup plan must be able to recover the database in the event of a server failure.
Find the most common value in each column of a table with two columns.
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SQL Problems
Given a table with two columns, find the most common value in each column using a SQL query.