Update large number of row in MySQL table

Question

I'm using relational database(MySQL 5.7). On this database i have a table called customer_transaction. On this table i have 4 columns: id, customer_id, type, amount

|id|customer_id |type     |amount|
|--|------------|---------|------|
|1 |44          |Credit   |50    |
|2 |44          |Credit   |20    |
|3 |44          |Debit    |30    |
|4 |10          |Credit   |30    |

now i am introduce a new balance column(current balance) on this table like below.

|id|customer_id |type     |amount|balance|
|--|------------|---------|------|-------|
|1 |44          |Credit   |50    |50     |
|2 |44          |Credit   |20    |70     |
|3 |44          |Debit    |30    |40     |
|4 |10          |Debit    |30    |-30    |

The problem is, on the customer transaction table, their was nearly millions of row and all balance column was 0.00.

So i want to re-sync all balance data. But i'm confused how to recalculate and update all those row. Can i update this by MySQL query or calculate and update from my application (Laravel-PHP).

Answer 1

In MySQL 5.x, where window functions are not available, an option uses a correlated subquery to compute the balance:

update customer_transaction ct
inner join (
    select 
        id, 
        (
            select sum(case type when 'Credit' then amount when 'Debit' then -amount end)
            from customer_transaction ct2
            where ct2.customer_id = ct1.customer_id and ct2.id <= ct1.id
        ) balance
    from customer_transaction ct1
) ctx on ctx.id = ct.id
set ct.balance = ctx.balance