SELECT
CUSTOMERS.ID
FROM CUSTOMERS
WHERE (SELECT SUM (PAYMENT .FISH_PRICE) FROM PAYMENT WHERE PAYMENT.CUSTOMER_ID = CUSTOMERS.ID AND PAYMENT.DATE_BEGIN >= : DATE_BEGIN AND PAYMENT.DATE_END <= :DATE_END) > '20000'
Untested :)
Uuuups sorry only payment table
SELECT
PAYMENT.CUSTOMER_ID,
SUM(PAYMENT.FISH_PRICE)
FROM PAYMENT
WHERE PAYMENT.DATE_BEGIN >= :DATE_BEGIN AND PAYMENT.DATE_END <= :DATE_END
GROUP BY PAYMENT.CUSTOMER_ID
HAVING
SUM(PAYMENT.FISH_PRICE) > '20000'
Still untested :)