Create a Cumulative Sum Column in MySQL

MySQL 8.0/MariaDB supports windowed SUM(col) OVER():

SELECT *, SUM(cnt) OVER(ORDER BY id) AS cumulative_sum
FROM tab;

Output:

┌─────┬──────┬────────────────┐
│ id  │ cnt  │ cumulative_sum │
├─────┼──────┼────────────────┤
│  1  │ 100  │            100 │
│  2  │  50  │            150 │
│  3  │  10  │            160 │
└─────┴──────┴────────────────┘

db<>fiddle