Yield Change Year over Year

For each farm and crop, return the change in tons versus the previous year for which that farm and crop has data. Show only rows that have a previous year. Order by farm name, crop, year.

Table schema

Farms(farm_id INT PRIMARY KEY, name VARCHAR(20), region VARCHAR(10))
Harvests(harvest_id INT PRIMARY KEY, farm_id INT, crop VARCHAR(10), year INT, tons INT, hectares INT)

Sample data

Farms
farm_id | name | region
1 | Green Acres | North
2 | Sun Fields | North
3 | River Bend | South

Harvests
harvest_id | farm_id | crop | year | tons | hectares
1 | 1 | Wheat | 2024 | 100 | 20
2 | 1 | Wheat | 2025 | 120 | 20
3 | 2 | Rice | 2025 | 90 | 10
4 | 2 | Wheat | 2025 | 60 | 10
5 | 3 | Rice | 2024 | 80 | 16
6 | 3 | Rice | 2025 | 64 | 16