Oracle 18c

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create table table1
(
	id number,
	contractdatetime date,
	Attr3 varchar2(100),
	Attr4 varchar2(100),
	Attr5 varchar2(100)
);
insert into table1 values (1, date '2000-01-01', 'a', 'a', 'a');
1 rows affected

insert into table1 values (2, date '2000-01-01', 'b', 'b', 'b');
1 rows affected

insert into table1 values (2, date '2000-01-02', null, null, null);
1 rows affected

insert into table1 values (3, date '2000-01-02', 'Oracle', 'Oracle', 'Oracle');
1 rows affected

select
	id,
	--Format the number
	trim(to_number(
		--Sum per group.
		sum(
			--Convert to a number.
			to_number(
				--Get the first 14 bytes. This seems to be the maximum that SQL Server can handle
				--before it runs into math errors.
				substr(
					--Hash the value.
					standard_hash(
						--Concatenate the values using (hopefully) unique strings to separate the
						--columns and represent NULLs (because the hashing functions treat nulls differently.)
						nvl(to_char(contractdatetime, 'YYYY-MM-DD HH24:MI:SS'), 'null') || 
						'-1-' || nvl(attr3, 'null') || '-2-' || nvl(attr3, 'null') || '-3-' || nvl(attr3, 'null')
						, 'MD5')
					, 1, 14)
				, 'xxxxxxxxxxxxxxxxxxxx'))
		, '99999999999999999999')) hash
from table1
group by id
order by 1;


ID
HASH


1
50696302970576522

2
69171702324546493

3
50787287321473273