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2082. The Number of Rich Customers

English Version

题目描述

Table: Store

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

 

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

The query 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.

解法

SQL

# Write your MySQL query statement below
SELECT
    COUNT(DISTINCT(customer_id)) AS rich_count
FROM
    Store
WHERE
    amount > 500;