Combining Customer Orders with INNER JOIN

This challenge focuses on using the INNER JOIN clause in SQL to combine data from two related tables. Understanding how to join tables is fundamental to relational database querying, allowing you to retrieve information that spans multiple tables based on shared columns. You'll be tasked with writing a SQL query to retrieve customer order information by joining a Customers table with an Orders table.

Problem Description

You are given two tables: Customers and Orders. The Customers table contains information about customers, and the Orders table contains information about their orders. The tables are related by a common column: CustomerID.

What needs to be achieved:

Write a SQL query that retrieves the customer's name, order ID, and order date for all orders placed by customers. The query should return a result set containing these three pieces of information, combining data from both tables.

Key Requirements:

• The query must use an INNER JOIN clause to combine the Customers and Orders tables.
• The join condition must be based on the CustomerID column, ensuring that only orders placed by existing customers are included.
• The result set must include the customer's name (from the Customers table), the order ID (from the Orders table), and the order date (from the Orders table).
• The column aliases should be used to clearly identify the columns in the result set (e.g., Customers.Name AS CustomerName, Orders.OrderID, Orders.OrderDate).

Expected Behavior:

The query should return a table with the following columns: CustomerName, OrderID, and OrderDate. Each row in the table should represent a single order placed by a customer, containing the customer's name, the order ID, and the order date. Only orders associated with valid customers in the Customers table should be included in the result.

Edge Cases to Consider:

• What happens if a customer in the Customers table has no orders in the Orders table? (These should not be included in the result due to the INNER JOIN).
• What happens if an order in the Orders table has a CustomerID that does not exist in the Customers table? (These should not be included in the result due to the INNER JOIN).

Examples

Example 1:

Customers Table:
CustomerID | Name
---------- | --------
1          | Alice
2          | Bob
3          | Charlie

Orders Table:
OrderID | CustomerID | OrderDate
-------- | ---------- | ----------
101     | 1          | 2023-01-15
102     | 2          | 2023-02-20
103     | 1          | 2023-03-10

Output:
CustomerName | OrderID | OrderDate
------------- | -------- | ----------
Alice         | 101     | 2023-01-15
Bob           | 102     | 2023-02-20
Alice         | 103     | 2023-03-10

Explanation: The query successfully joins the Customers and Orders tables based on CustomerID, returning the customer's name, order ID, and order date for each order.

Example 2:

Customers Table:
CustomerID | Name
---------- | --------
1          | Alice
2          | Bob

Orders Table:
OrderID | CustomerID | OrderDate
-------- | ---------- | ----------
101     | 1          | 2023-01-15
102     | 3          | 2023-02-20  -- CustomerID 3 doesn't exist in Customers table

Output:
CustomerName | OrderID | OrderDate
------------- | -------- | ----------
Alice         | 101     | 2023-01-15

Explanation: The order with CustomerID 3 is excluded from the result because there is no corresponding customer in the Customers table. The INNER JOIN ensures that only matching records are returned.

Constraints

• The Customers table has at least 10 rows and the Orders table has at least 20 rows.
• Both tables have a CustomerID column of integer type.
• The Customers table has a Name column of string type.
• The Orders table has an OrderID column of integer type and an OrderDate column of date type.
• The query must execute within 5 seconds on a standard database server.

Notes

• Consider using aliases for table names to make the query more readable.
• The INNER JOIN clause is crucial for this problem. Other join types (e.g., LEFT JOIN, RIGHT JOIN) will not produce the desired result.
• Pay close attention to the column names and data types when constructing the query.
• Think about how the INNER JOIN handles cases where there are no matching records in one of the tables.
• Pseudocode:

SELECT
    Customers.Name AS CustomerName,
    Orders.OrderID,
    Orders.OrderDate
FROM
    Customers
INNER JOIN
    Orders
ON
    Customers.CustomerID = Orders.CustomerID;