Erai destul de aproape:

SELECT CONT, RULAJ_INITIAL_DEBITOR, RULAJ_INITIAL_CREDITOR,
    RULAJ_CURENT_DEBITOR, RULAJ_CURENT_CREDITOR,
    RULAJ_TOTAL_DEBITOR, RULAJ_TOTAL_CREDITOR,
    CASE WHEN RULAJ_TOTAL_DEBITOR>RULAJ_TOTAL_CREDITOR
        THEN RULAJ_TOTAL_DEBITOR-RULAJ_TOTAL_CREDITOR
        ELSE 0
    END AS SOLD_DEBITOR,
    CASE WHEN RULAJ_TOTAL_CREDITOR>RULAJ_TOTAL_DEBITOR
        THEN RULAJ_TOTAL_CREDITOR-RULAJ_TOTAL_DEBITOR
        ELSE 0
    END AS SOLD_CREDITOR
FROM (
    SELECT COALESCE(S.CONT, D.CONT, C.CONT, A.CONT, B.CONT) AS CONT,
        ISNULL(S.SOLD_DEBITOR,0)+ISNULL(D.RULAJ_INITIAL_DEBITOR,0) AS RULAJ_INITIAL_DEBITOR,
        ISNULL(S.SOLD_CREDITOR,0)+ISNULL(C.RULAJ_INITIAL_CREDITOR,0) AS RULAJ_INITIAL_CREDITOR,
        ISNULL(A.RULAJ_CURENT_DEBITOR,0) AS RULAJ_CURENT_DEBITOR,
        ISNULL(B.RULAJ_CURENT_CREDITOR,0) AS RULAJ_CURENT_CREDITOR,
        ISNULL(S.SOLD_DEBITOR,0)+ISNULL(D.RULAJ_INITIAL_DEBITOR,0)
            +ISNULL(A.RULAJ_CURENT_DEBITOR,0) AS RULAJ_TOTAL_DEBITOR,
        ISNULL(S.SOLD_CREDITOR,0)+ISNULL(C.RULAJ_INITIAL_CREDITOR,0)
            +ISNULL(B.RULAJ_CURENT_CREDITOR,0) AS RULAJ_TOTAL_CREDITOR
    FROM SOLDURI_INITIALE S

    FULL OUTER JOIN (
        SELECT CONTDB AS CONT, SUM(LEI) AS RULAJ_INITIAL_DEBITOR
        FROM NOTE_CONTABILE WHERE DATADOC BETWEEN '20070101' AND '20070131' GROUP BY CONTDB
    ) D ON S.CONT=D.CONT

    FULL OUTER JOIN (
        SELECT CONTCR AS CONT, SUM(LEI) AS RULAJ_INITIAL_CREDITOR
        FROM NOTE_CONTABILE WHERE DATADOC BETWEEN '20070101' AND '20070131' GROUP BY CONTCR
    ) C ON C.CONT=ISNULL(S.CONT,D.CONT)

    FULL OUTER JOIN (
        SELECT CONTDB AS CONT, SUM(LEI) AS RULAJ_CURENT_DEBITOR
        FROM NOTE_CONTABILE WHERE DATADOC BETWEEN '20070201' AND '20070228' GROUP BY CONTDB
    ) A ON A.CONT=COALESCE(S.CONT,D.CONT,C.CONT)

    FULL OUTER JOIN (
        SELECT CONTCR AS CONT, SUM(LEI) AS RULAJ_CURENT_CREDITOR
        FROM NOTE_CONTABILE WHERE DATADOC BETWEEN '20070201' AND '20070228' GROUP BY CONTCR
    ) B ON B.CONT=COALESCE(S.CONT,D.CONT,C.CONT,A.CONT)
) X
ORDER BY CONT

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