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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).

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Hasan Hafiz Pasha
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    Yes, you can do it. Use a session variable to hold the running balance from the previous row, and either add or subtract depending on whether the type is `Credit` or `Debit`. When the customer_id` changes you set the variable back to `0`. – Barmar May 21 '20 at 21:11

1 Answers1

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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
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  • But their is a problem. We are doing those process on a live server and it take's some times to execute. i think, during that execution time, my transaction table remains locked. Is their any way to preventing locking. – Hasan Hafiz Pasha May 22 '20 at 09:08