# 1821. Find Customers With Positive Revenue this Year

<https://leetcode.com/problems/find-customers-with-positive-revenue-this-year>

## Description

Table: `Customers`

```
+--------------+------+
| Column Name  | Type |
+--------------+------+
| customer\_id  | int  |
| year         | int  |
| revenue      | int  |
+--------------+------+
(customer\_id, year) is the primary key for this table.
This table contains the customer ID and the revenue of customers in different years.
Note that this revenue can be negative.
```

Write an SQL query to report the customers with **postive revenue** in the year 2021.

Return the result table in **any order**.

The query result format is in the following example:

```
Customers
+-------------+------+---------+
| customer\_id | year | revenue |
+-------------+------+---------+
| 1           | 2018 | 50      |
| 1           | 2021 | 30      |
| 1           | 2020 | 70      |
| 2           | 2021 | -50     |
| 3           | 2018 | 10      |
| 3           | 2016 | 50      |
| 4           | 2021 | 20      |
+-------------+------+---------+
Result table:
+-------------+
| customer\_id |
+-------------+
| 1           |
| 4           |
+-------------+
Customer 1 has revenue equal to 30 in year 2021.
Customer 2 has revenue equal to -50 in year 2021.
Customer 3 has no revenue in year 2021.
Customer 4 has revenue equal to 20 in year 2021.
Thus only customers 1 and 4 have postive revenue in year 2021.
```

## ac

```java
```