how to perform operations in queries programatically?

Question

How to do the operation w_balance = w_balance + amount in the query String? One way is to perform the operation outside the Query String. But is there a way to do that directly? Here, amount is the new amount I would want to add or subtract from the w_balance .

My database is postgresql.

String SQL = "update walletapp.users_acc set w_balance = w_balance + amount where kyc_id = :sender_id";

I used - String SQL = "update walletapp.users_acc set w_balance = w_balance + :amount where kyc_id = :sender_id"; which solved my problem.

Answer 1

Here is a simple example of an assignation of a value an the usage of it :

int i = 0;
System.out.println(i = 5);
String s = "The Value is " + (i = 4);
System.out.println(s);
System.out.println(i);

This will output

5

The Value is 4

4

So you see that you can set the variable an recover it at the same time, this is just some operator priority

Answer 2

如@a_horse_with_no_name所示， set w_balance = w_balance + :amount对我set w_balance = w_balance + :amount 。

Answer 3

Assing it to a variable or do it directly. A good way to do it is using String.format:

String SQL = String.format("update walletapp.users_acc set w_balance = %d where kyc_id = :sender_id", w_balance + amount);