Add a Column and Backfill It

Add a grade column (CHAR(1)) to Employees and fill it: 'A' for salary >= 70000, 'B' for salary >= 50000, otherwise 'C'.

Table schema

Employees(id INT PRIMARY KEY, name VARCHAR(50), salary INT)

Sample data

id | name | salary
1 | Alice | 80000
2 | Bob | 55000
3 | Carol | 30000