ID|ID_OPERATION|ID_CURRENCY|
1 |     5      |    1      |
2 |     7      |    1      |
3 |     5      |    2      |
4 |     7      |    2      |

ID|ID_OPER|COUNT|PRICE|
1 |   1   |  1  | 10  |
2 |   2   |  1  | 10  |
3 |   3   |  1  | 10  |
4 |   4   |  1  | 10  |

select sum (OPERATION_MODELS.COUNT*OPERATION_MODELS.PRICE) where OPERATIONS.ID_OPERATION=5  group by OPERATIONS.ID_CURRENCY минус select sum (OPERATION_MODELS.COUNT*OPERATION_MODELS.PRICE) where OPERATIONS.ID_OPERATION=7  group by OPERATIONS.ID_CURRENCY

SELECT
SUM(OPERATION_MODELS.COUNT*OPERATION_MODELS.PRICE) FILTER(WHERE OPERATIONS.ID_OPERATION=5)
-
SUM(OPERATION_MODELS.COUNT*OPERATION_MODELS.PRICE) FILTER(WHERE OPERATIONS.ID_OPERATION=7)
FROM ...
group by OPERATIONS.ID_CURRENCY