using mysql calculate balance of each currency where credit and debit in same column?
I would try something like this to get the results that you are looking for. What this is doing is determining how to add everything up based on the record being a credit or debit and subtracting the debit values instead of adding them.

SELECT CLIENT_ID,
       SUM(IF(currency='USD',IF(ACTION_TYPE='credit',ACTION_AMOUNT, - ACTION_AMOUNT))) as USD_balance,
       SUM(IF(currency='EURO',IF(ACTION_TYPE='credit',ACTION_AMOUNT, - ACTION_AMOUNT))) as EURO_balance,
       SUM(IF(currency='DR',IF(ACTION_TYPE='credit',ACTION_AMOUNT, - ACTION_AMOUNT))) as DR_balance
FROM my_table
GROUP BY CLIENT_ID,currency