SQL Server : joins new syntax(ANSI vs. non-ANSI SQL JOIN syntax) - sql

Question

I have tried to convert old MS sql join syntax to new join syntax but number of rows in the results not matching.
Original SQL:
select
b.Amount
from
TableA a, TableB b,TableC c, TableD d
where
a.inv_no *= b.inv_no and
a.inv_item *= b.inv_item and
c.currency *= b.cash_ccy and
d.tx_code *= b.cash_receipt
Converted SQL:
SELECT
b.AMOUNT
FROM
(TableA AS a
LEFT OUTER JOIN
TableB AS b ON a.INV_NO = b.INV_NO
AND a.inv_item = b.inv_item
LEFT OUTER JOIN
TableC AS c ON c.currency = b.cash_ccy)
LEFT OUTER JOIN
TableD as d ON d.tx_code = b.cash_receipt
Findings
Results are same on both original SQL and modified SQL upto joining of 3 tables but when joining the fourth table (TableD) to the modified SQL, the number of rows returned is different.

Answer 1

The order of fields within predicates is important when using SQL Server's (deprecated) proprietary ANSI 89 join syntax *= or =*
So while
SELECT *
FROM TableA AS A
LEFT JOIN TableB AS B
ON A.ColA = B.ColB;
Is exactly the same as
SELECT *
FROM TableA AS A
LEFT JOIN TableB AS B
ON B.ColB = A.ColA; -- NOTE ORDER HERE
The eqivalent
SELECT *
FROM TableA AS A, TableB AS b
WHERE A.ColA *= B.ColB;
Is not the same as
SELECT *
FROM TableA AS A, TableB AS b
WHERE B.ColA *= A.ColB;
This last query's ANSI 92 equivalent would be
SELECT *
FROM TableA AS A
RIGHT JOIN TableB AS B
ON A.ColA = B.ColB;
Or if you dislike RIGHT JOIN as much as I do you would probably write:
SELECT *
FROM TableB AS B
LEFT OUTER JOIN TableA AS A
ON B.ColB = A.ColA;
So actually the equivalent query in ANSI 92 join syntax would involve starting with TableA, TableC and TableD (since these are the leading fields in the original WHERE Clause). Then since there is no direct link between the three, you end up with a cross join
SELECT b.Amount
FROM TableA AS a
CROSS JOIN TableD AS d
CROSS JOIN TableC AS c
LEFT JOIN TableB AS B
ON c.currency = b.cash_ccy
AND d.tx_code = b.cash_receipt
AND a.INV_NO = b.INV_NO
AND a.inv_item = b.inv_item;
This is the equivalent rewrite, and explans the difference in the number of rows
WORKING EXAMPLE
Needs to be run on SQL Server 2008 or earlier with compatibility level 80 or less
-- SAMPLE DATA --
CREATE TABLE #TableA (Inv_No INT, Inv_item INT);
CREATE TABLE #TableB (Inv_No INT, Inv_item INT, cash_ccy INT, cash_receipt INT, Amount INT);
CREATE TABLE #TableC (currency INT);
CREATE TABLE #TableD (tx_code INT);
INSERT #TableA (inv_no, inv_item) VALUES (1, 1), (2, 2);
INSERT #TableB (inv_no, inv_item, cash_ccy, cash_receipt, Amount) VALUES (1, 1, 1, 1, 1), (2, 2, 2, 2, 2);
INSERT #TableC (currency) VALUES (1), (2), (3), (4);
INSERT #TableD (tx_code) VALUES (1), (2), (3), (4);
-- ORIGINAL QUERY(32 ROWS)
SELECT
b.Amount
FROM
#TableA a, #TableB b,#TableC c, #TableD d
WHERE
a.inv_no *= b.inv_no and
a.inv_item *= b.inv_item and
c.currency *= b.cash_ccy and
d.tx_code *= b.cash_receipt
-- INCORRECT ANSI 92 REWRITE (2 ROWS)
SELECT b.AMOUNT
FROM #TableA AS a
LEFT OUTER JOIN #TableB AS b
ON a.INV_NO = b.INV_NO
and a.inv_item = b.inv_item
LEFT OUTER JOIN #TableC AS c
ON c.currency = b.cash_ccy
LEFT OUTER JOIN #TableD as d
ON d.tx_code = b.cash_receipt;
-- CORRECT ANSI 92 REWRITE (32 ROWS)
SELECT b.Amount
FROM #TableA AS a
CROSS JOIN #TableD AS d
CROSS JOIN #TableC AS c
LEFT JOIN #TableB AS B
ON c.currency = b.cash_ccy
AND d.tx_code = b.cash_receipt
AND a.INV_NO = b.INV_NO
AND a.inv_item = b.inv_item;