We have a monthly snapshot table that records each account's delinquency status and balance every month. For example, account 101 was current in January, 30 days past due in February, and 60 days past due in March. I want to see, by balance, what share of current balances rolled into 30 days past due each month. How would you write the SQL, and how would you read the results?

我们有一张账户月度快照表，每个月记录每个账户的逾期状态和余额。比如账户101一月正常，二月逾期30天，三月逾期60天。我想按余额看每个月从正常滚到逾期30天的比例。你怎么写SQL？结果怎么解读？