Is The Number of Rich Customers easy or hard?

The Number of Rich Customers is categorized as an Easy SQL problem. It mainly tests your understanding of filtering rows and counting unique values using COUNT(DISTINCT) or GROUP BY.

The Number of Rich Customers Python/Java solution

This is a SQL database problem, so the primary solution is written in MySQL or another SQL dialect. In application code such as Python or Java, you would execute the SQL query against the database and retrieve the resulting count.

How to solve The Number of Rich Customers in O(n)?

Filter rows with amount > 500 and count distinct customer IDs. Example: SELECT COUNT(DISTINCT customer_id) FROM Store WHERE amount > 500;. The database processes the table once, making the solution O(n) time with efficient built‑in aggregation.

What is the best approach for The Number of Rich Customers?

The most efficient solution filters rows where amount > 500 and counts unique customers using COUNT(DISTINCT customer_id). This runs in O(n) time because the database scans the table once and performs a distinct aggregation. It is also the shortest and most common SQL solution used in interviews.

Is The Number of Rich Customers asked at Google/Amazon/Meta?

This type of SQL filtering and aggregation problem appears in database interview rounds at companies like Amazon, Google, and Meta. While the exact question may vary, counting distinct entities after applying a filter is a common pattern tested in data engineering and backend interviews.

What data structure is used in The Number of Rich Customers?

The problem relies on relational database operations rather than traditional data structures. Internally, SQL engines use hashing or sorting to implement DISTINCT and aggregation, but from a query perspective the main concepts are filtering and counting unique values.

What is the time complexity of The Number of Rich Customers?

The query typically runs in O(n) time where n is the number of rows in the Store table. The database scans each row to check the amount condition and performs a DISTINCT aggregation on customer_id. Space usage depends on the query plan but is usually minimal.

2082. The Number of Rich Customers - Practice Online

Table: Store

+-------------+------+
| Column Name | Type |
+-------------+------+
| bill_id     | int  |
| customer_id | int  |
| amount      | int  |
+-------------+------+
bill_id is the primary key (column with unique values) for this table.
Each row contains information about the amount of one bill and the customer associated with it.

Write a solution to report the number of customers who had at least one bill with an amount strictly greater than 500.

The result format is in the following example.

Example 1:

Input: 
Store table:
+---------+-------------+--------+
| bill_id | customer_id | amount |
+---------+-------------+--------+
| 6       | 1           | 549    |
| 8       | 1           | 834    |
| 4       | 2           | 394    |
| 11      | 3           | 657    |
| 13      | 3           | 257    |
+---------+-------------+--------+
Output: 
+------------+
| rich_count |
+------------+
| 2          |
+------------+
Explanation: 
Customer 1 has two bills with amounts strictly greater than 500.
Customer 2 does not have any bills with an amount strictly greater than 500.
Customer 3 has one bill with an amount strictly greater than 500.