add 1821

Author: fishercoder1534

Diff for: database/_1821.sql

@@ -0,0 +1,2 @@
+-- Write your PostgreSQL query statement below
+select customer_id from Customers where revenue > 0 and year = 2021;

Diff for: paginated_contents/database/README.md

@@ -8,6 +8,7 @@
 | 2072 |[The Winner University](https://leetcode.com/problems/the-winner-university/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_2072.sql)                                || Easy |
 | 2026 |[Low-Quality Problems](https://leetcode.com/problems/low-quality-problems/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_2026.sql)                                || Easy |
 | 1978 |[Employees Whose Manager Left the Company](https://leetcode.com/problems/employees-whose-manager-left-the-company/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1978.sql)                                || Easy |
+| 1821 |[Find Customers With Positive Revenue this Year](https://leetcode.com/problems/find-customers-with-positive-revenue-this-year/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1821.sql)                                || Easy |
 | 1809 |[Ad-Free Sessions](https://leetcode.com/problems/ad-free-sessions/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1809.sql)                                || Easy |
 | 1795 |[Rearrange Products Table](https://leetcode.com/problems/rearrange-products-table/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1795.sql)                                || Easy |
 | 1789 |[Primary Department for Each Employee](https://leetcode.com/problems/primary-department-for-each-employee/)| [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/database/_1789.sql)                                || Easy |