select  b1.ORDER_CUSTOMER, b1.SOURCE_LOCATION, b1.DEST_LOCATION
from  table b1
 JOIN table a1 ON b1.SOURCE_LOCATION=a1.LOCATION_ID 
 JOIN  table a2 ON b1.DEST_LOCATION=a2.LOCATION_ID
where a1.PROVINCE_CODE='77'
and a2.PROVINCE_CODE='50'

declare @b1 table (
ORDER_CUSTOMER int,	SOURCE_LOCATION int, 	DEST_LOCATION int);
insert into @b1 
values
(100,	70,	40),
(200,	68,	70),
(201,	40,	33),
(201,	50,	41)
;
select * from @b1

declare @a table (
LOCATION_ID int,	LOCATION_NAME nvarchar(100),	PROVINCE_CODE int);
insert into @a 
values

(70,	'МОСКВА',	77),
(68,	'СПБ',	77),
(40,	'ТАМБОВ',	50),
(50,	'ВОРОНЕЖ',	50)
;
select * from @a;

select  b1.ORDER_CUSTOMER, b1.SOURCE_LOCATION, b1.DEST_LOCATION
from   @b1 b1
 JOIN @a a1 ON b1.SOURCE_LOCATION=a1.LOCATION_ID 
 JOIN @a a2 ON b1.DEST_LOCATION=a2.LOCATION_ID
where a1.PROVINCE_CODE='77'
and a2.PROVINCE_CODE='50'