LeetCode 586. Customer Placing the Largest Number of Orders SQL Solution

Problem

LeetCode SQL Problem

586. Customer Placing the Largest Number of Orders

orders table

order_number	customer_number	order_date	required_date	shipped_date	status	comment
1	1	2017-04-09	2017-04-13	2017-04-12	Closed
2	2	2017-04-15	2017-04-20	2017-04-18	Closed
3	3	2017-04-16	2017-04-25	2017-04-20	Closed
4	3	2017-04-18	2017-04-28	2017-04-25	Closed

Solution

MySQL

Find the Customer Placing the Largest Number of Orders

SELECT customer_number
FROM orders
GROUP BY customer_number
ORDER BY COUNT(*) DESC
LIMIT 1;

This MySQL query retrieves the customer number of the customer who has placed the highest number of orders. It achieves this by grouping the orders based on customer numbers, counting the number of orders for each customer, ordering the groups in descending order by the order count, and then limiting the result to only one row.

Here's a breakdown of the query:

1. SELECT customer_number: This part of the query specifies that you want to select the "customer_number" column from the "orders" table. This column presumably contains unique identifiers for customers.

2. FROM orders: This part indicates that you are fetching data from the "orders" table, assuming it contains information about customer orders.

3. GROUP BY customer_number: This clause groups the rows in the "orders" table based on the unique values in the "customer_number" column. Each group represents orders placed by the same customer.

4. ORDER BY COUNT(*) DESC: This clause specifies how the grouped results should be ordered. It orders the groups in descending order based on the count of rows in each group. The COUNT(*) function counts the number of rows (orders) in each customer group. This ensures that customers with the highest order count will appear first.

5. LIMIT 1: This clause restricts the result to only one row. Since the groups are ordered by order count in descending order, this effectively retrieves the customer number of the customer with the highest number of orders.

In summary, the query identifies the customer who has placed the most orders by grouping orders by customer number, counting the orders for each customer, ordering the groups by order count in descending order, and then limiting the result to a single row using the LIMIT 1 clause.

TSQL

Find the Customer Placing the Largest Number of Orders

SELECT TOP 1 customer_number
FROM orders
GROUP BY customer_number
ORDER BY count(*) DESC

The above SQL query is used to retrieve the customer number of the customer who has placed the highest number of orders. Let's break down the query step by step:

1. SELECT TOP 1 customer_number: This part of the query specifies that you want to select the top (highest) result, limited to 1 row, and retrieve the "customer_number" column.

2. FROM orders: This part indicates that you are fetching data from the "orders" table. It assumes that the "orders" table contains information about customer orders, including the "customer_number" column.

3. GROUP BY customer_number: This clause groups the rows in the "orders" table based on the unique values in the "customer_number" column. This means that all orders placed by the same customer will be considered as a single group.

4. ORDER BY count(*) DESC: This clause specifies how the grouped results should be ordered. Here, it orders the groups in descending order based on the count of rows in each group. The count(*) function counts the number of rows in each group. This is done in descending order, so the group with the highest count (indicating the customer with the most orders) will appear first.

Putting it all together, the query retrieves the customer number of the customer who has placed the highest number of orders. It achieves this by grouping the orders by customer number, counting the number of orders for each customer, and then ordering the groups in descending order based on the order count. The TOP 1 clause ensures that only the top result (customer with the most orders) is returned.

Query Output

customer_number
3