Вы пытались заменить (менее читаемый imho) синтаксис объединения на обычный INNER JOINS
?
SELECT TableA.serialNo
FROM TableA
INNER JOIN (
SELECT MAX(TableB.lotNo) AS lotNo
,TableA.codeA
,TableA.codeB
FROM TableA
INNER JOIN TableB ON TableA.codeA = TableB.codeA
AND TableA.codeB = TableB.codeB
WHERE LEN(TableA.openDate) > 0
OR TableA.openDate IS NOT NULL
GROUP BY
TableA.codeA, TableA.codeB
) a ON TableA.lotNo < a.lotNo
AND TableA.codeA = a.codeA
AND TableA.codeB = a.codeB
WHERE LEN(TableA.endDate) = 0
OR TableA.endDate IS NULL
или переписать условия
SELECT a1.serialNo
FROM TableA a1
INNER JOIN (
SELECT MAX(b.lotNo) AS lotNo
, a.codeA
, a.codeB
FROM TableA a
INNER JOIN TableB b ON a.codeA = b.codeA
AND a.codeB = b.codeB
WHERE a.openDate IS NOT NULL
GROUP BY
a.codeA, a.codeB
) a2 ON a1.lotNo < a2.lotNo
AND a1.codeA = a2.codeA
AND a1.codeB = a2.codeB
WHERE LEN(COALESCE(a1.endDate, '')) = 0