is not distinct from in join on clause oracle - sql

Question

I have a query structured with the left outer join like so:
left outer JOIN GA_LOAN GA
ON LOAN.LOAN_TYPE = GA.LOAN_TYP
AND LOAN.DT = GA.GUARANTY_DT
AND LOAN.FFEL_DUP_ID = GA.SEP_LOAN_IND
AND LOAN.SCH_BR_CODE = GA.ORIG_SCHL_CD
AND STU.CURR_SSN = GA.STU_SSN
AND STU.DOB = GA.DOB
and stu.curr_fst = ga.stu_first_nam
--and (plus_bor.curr_ssn is not distinct from ga.plus_brwr_ssn )
When I add the commented out line, I get the following error.
ORA-00908: missing NULL keyword
00908. 00000 - "missing NULL keyword"
*Cause:
*Action:
is not distinct from works fine in this structure in DB2, but Oracle is giving me issues. Any suggestions?
I get no errors if I replaced is not distinct from with a = but that isn't the same logically.
is not distinct from with give a match if both values are null, where as = would not match in this case.

Answer 1

The simplest way to emulate IS [ NOT ] DISTINCT FROM in Oracle is by using DECODE:
-- a IS DISTINCT FROM b
DECODE(a, b, 1, 0) = 0
-- a IS NOT DISTINCT FROM b
DECODE(a, b, 1, 0) = 1
This is what you're getting when you're using jOOQ's SQL dialect translator. A dbfiddle for this:
WITH t (x) AS (
SELECT 1 FROM dual UNION ALL
SELECT 2 FROM dual UNION ALL
SELECT null FROM dual
)
SELECT
t1.x AS x1,
t2.x AS x2,
DECODE(t1.x, t2.x, 1, 0) AS not_distinct
FROM t t1, t t2
ORDER BY 1, 2
Yields:
X1 | X2 | NOT_DISTINCT
-----+------+-------------
1 | 1 | 1
1 | 2 | 0
1 | null | 0
2 | 1 | 0
2 | 2 | 1
2 | null | 0
null | 1 | 0
null | 2 | 0
null | null | 1

Answer 2

You could emulate IS DISTINCT FROM by using NOT EXISTS combined with INTERSECT:
plus_bor.curr_ssn IS DISTINCT FROM ga.plus_brwr_ssn
<=>
NOT EXISTS (SELECT plus_bor.curr_ssn FROM dual INTERSECT
SELECT ga.plus_brwr_ssn FROM dual);
Example:
WITH cte(a,b) AS (
SELECT 1, NULL FROM dual UNION ALL
SELECT 1,2 FROM dual UNION ALL
SELECT 1,1 FROM dual UNION ALL
SELECT NULL, 1 FROM dual UNION ALL
SELECT NULL, NULL FROM dual
)
SELECT *
FROM cte
WHERE NOT EXISTS (SELECT a FROM dual INTERSECT
SELECT b FROM dual)
Rextester Demo
Output:
A B
------------
1 NULL
1 2
NULL 1
And in your case IS NOT DISTINCT FROM is simply EXISTS:
plus_bor.curr_ssn IS NOT DISTINCT FROM ga.plus_brwr_ssn
<=>
EXISTS (SELECT plus_bor.curr_ssn FROM dual INTERSECT
SELECT ga.plus_brwr_ssn FROM dual);
Example:
WITH cte(a,b) AS (
SELECT 1, NULL FROM dual UNION ALL
SELECT 1,2 FROM dual UNION ALL
SELECT 1,1 FROM dual UNION ALL
SELECT NULL, 1 FROM dual UNION ALL
SELECT NULL, NULL FROM dual
)
SELECT *
FROM cte
WHERE EXISTS (SELECT a FROM dual INTERSECT
SELECT b FROM dual);
Output:
A B
1 1
NULL NULL
Rextester Demo2
ADDENDUM
This approach has one big advantage over COALESCE/NVL approach as proposed in comments.
You don't have to think about default neutral value dependent on datatype.
For example if column is datatype DATE/INT/TEXT then you have to write something like:
coalesce(col1,DATE '1900-01-01') = coalesce(col2,DATE '1900-01-01')
coalesce(col1, 0) = coalesce(col2, 0)
coalesce(col1, ' ') = coalesce(col2, ' ')
There is of course slight chance of collision. For example:
coalesce(col1, 0) = coalesce(col2, 0)
=>
col1 = NULL
col2 = 0
and we have incorrect match!!!