definitely opens the transaction and locks it with for update.. Because you have to remember the current balance, you need to use the current balance of the user
if you do not need to use the current balance of the user, you can try the atomic operation of sql:

update user set balance = balance-10 where user_id = xxx;

first of all, the operation of the user account needs to be locked, regardless of consumption or recharge. For example, when recharging, you need to obtain an account lock first. After success, other operations, such as consumption, cannot acquire the account lock and can only wait for the lock to be released.
secondly, you can add a condition to the SQL statement to achieve the failure effect of account changes, for example:

update user set balance = balance+5 where user_id = xxx AND balance = 5;

add that the original balance is 5, but now you want to recharge 5, then add balance=5 to the condition, so that if the balance has been modified, the update fails. So as not to overwrite the data.

again, the change of user balance needs to be streamlined, and when the amount does not match, it can be traced back through pipelining.

optimistic lock.
add a version number field to the balance table. For each operation, the balance version number is + 1. Before updating the balance, get the version number first. Update process:

select version from table order by version desc limit 1;

update table set balace = xx,version = version + 1 where version = xx;

if the update fails (returns 0), continue the above operation, which is called spin lock.

increase the balance

set autocommit=0;
update <table> set balance=balance+<xxx> where id=<id>;
select * from <table> where id=<id>
commit;

make sure that the above two statements are executed in the same transaction. Finally, the operation is done in the program.

• balance-< xxx > is the balance before the increase
• balance is the increased balance

withdraw

set autocommit=0;
update <table> set balance=balance-<xxx> where id=<id> and balance>=<xxx>;
select * from <table> where id=<id>;
commit;

make sure that the above two statements are executed in the same transaction. Finally, the operation is done in the program.

• balance + < xxx > is the balance before withdrawal
• balance is the balance after withdrawal