由于 where 子句过滤器，右外连接似乎不起作用

为了稍微简化您的查询，您基本上有以下内容：

SELECT *
FROM
    [src_boss_entwicklung].[dbo].[tckopf] AS commission
RIGHT OUTER JOIN
    [src_boss_entwicklung].[dbo].[tckopf] AS originDocForCurrency
    ON commission.referenzid = originDocForCurrency.id
WHERE
    originDocForCurrency.id = 68
AND (commission.referenzid = 68 OR commission.referenzid = 68);

[src_boss_entwicklung].[dbo].[tckopf]在列中没有匹配项的地方commission.referenzid将为 NULL，这意味着这种情况：

AND (commission.referenzid = 68 OR commission.referenzid = 68);

这些行将不正确（因为NULL = 68计算结果为NULL）。这有效地使您RIGHT OUTER JOIN的INNER JOIN

我从来都不是RIGHT JOIN特别喜欢LEFT JOIN出现在同一个查询中时。为了连续性，我将重新排列查询以使所有外连接都离开外连接：

SELECT *
FROM
    [src_boss_entwicklung].[dbo].[tckopf] AS originDocForCurrency
LEFT OUTER JOIN
    [src_boss_entwicklung].[dbo].[tckopf] AS commission
    ON commission.referenzid = originDocForCurrency.id
LEFT OUTER JOIN
    [src_boss_entwicklung].[dbo].[devisen] AS currencies
    ON currencies.datum = (
            SELECT TOP 1 fc.datum
            FROM [src_boss_entwicklung].[dbo].[devisen] AS fc
            WHERE fc.datum <= originDocForCurrency.von
                AND fc.usd_brief IS NOT NULL AND fc.usd_brief > 0
                AND fc.usd_geld IS NOT NULL AND fc.usd_geld > 0
            ORDER BY fc.datum DESC
            )
WHERE
    originDocForCurrency.id = 68
AND (commission.referenzid = 68 OR commission.referenzid = 68);

但这并不能解决问题，因为您仍然有可能commission.referenzid将NULLLEFT OUTER JOIN 变成 INNER JOIN。您可以通过将谓词移动到 JOIN 条件来解决此问题：

SELECT *
FROM
    [src_boss_entwicklung].[dbo].[tckopf] AS originDocForCurrency
LEFT OUTER JOIN
    [src_boss_entwicklung].[dbo].[tckopf] AS commission
    ON commission.referenzid = originDocForCurrency.id
    AND     
    ( commission.referenzid = 68
        AND commission.btyp = 7
        AND ( commission.storno <> 1 OR commission.storno IS NULL )
        AND ( commission.proforma <> 1 OR commission.proforma IS NULL ) )
    OR
    ( commission.referenzid = 68
        AND commission.btyp = 8
        AND ( commission.storno <> 1 OR commission.storno IS NULL )
        AND ( commission.proforma <> 1 OR commission.proforma IS NULL ) 
    )

我也相当肯定这种情况可以简化为：

SELECT *
FROM
    [src_boss_entwicklung].[dbo].[tckopf] AS originDocForCurrency
LEFT OUTER JOIN
    [src_boss_entwicklung].[dbo].[tckopf] AS commission
    ON commission.referenzid = originDocForCurrency.id
    AND commission.referenzid = 68
    AND commission.btyp in (7, 8)
    AND ISNULL(commission.storno, 0) <> 1
    AND ISNULL(commission.proforma, 0) <> 1

进行最终查询：

SELECT
    commission.netto AS commissionNetValue,
    commission.r_art AS commissionDocClass,
    commission.waehrung AS commissionCurrency,
    currencies.usd_brief AS foreignCurrencyUSDAsk,
    currencies.usd_geld AS foreignCurrencyUSDBid,
    originDocForCurrency.r_art AS originDocForCurrencyDocClass,
    originDocForCurrency.poswert AS originDocForCurrencyCommission,
 (SELECT originDoc.poswert FROM [src_boss_entwicklung].[dbo].[tckopf] AS originDoc WHERE originDoc.id = 68) AS originDocCommission,
 (SELECT originDoc.r_art FROM [src_boss_entwicklung].[dbo].[tckopf] AS originDoc WHERE originDoc.id = 68) AS originDocClass,
 (SELECT originDoc.waehrung FROM [src_boss_entwicklung].[dbo].[tckopf] AS originDoc WHERE originDoc.id = 68) AS originDocCurrency
FROM
    [src_boss_entwicklung].[dbo].[tckopf] AS originDocForCurrency
LEFT OUTER JOIN
    [src_boss_entwicklung].[dbo].[tckopf] AS commission
    ON commission.referenzid = originDocForCurrency.id
    AND commission.referenzid = 68
    AND commission.btyp in (7, 8)
    AND ISNULL(commission.storno, 0) <> 1
    AND ISNULL(commission.proforma, 0) <> 1
LEFT OUTER JOIN
    [src_boss_entwicklung].[dbo].[devisen] AS currencies
    ON currencies.datum = (
            SELECT TOP 1 fc.datum
            FROM [src_boss_entwicklung].[dbo].[devisen] AS fc
            WHERE fc.datum <= originDocForCurrency.von
                AND fc.usd_brief IS NOT NULL AND fc.usd_brief > 0
                AND fc.usd_geld IS NOT NULL AND fc.usd_geld > 0
            ORDER BY fc.datum DESC
            )
WHERE
    originDocForCurrency.id = 68;

附录

正如评论中指出的那样，您不需要三个子选择，您可以只使用表中的列 aliased originDocForCurrency：

SELECT
    commission.netto AS commissionNetValue,
    commission.r_art AS commissionDocClass,
    commission.waehrung AS commissionCurrency,
    currencies.usd_brief AS foreignCurrencyUSDAsk,
    currencies.usd_geld AS foreignCurrencyUSDBid,
    originDocForCurrency.r_art AS originDocForCurrencyDocClass,
    originDocForCurrency.poswert AS originDocForCurrencyCommission,
    originDocForCurrency.poswert AS originDocCommission,
    originDocForCurrency.r_art AS originDocClass,
    originDocForCurrency.waehrung AS originDocCurrency
FROM
    [src_boss_entwicklung].[dbo].[tckopf] AS originDocForCurrency
LEFT OUTER JOIN
    [src_boss_entwicklung].[dbo].[tckopf] AS commission
    ON commission.referenzid = originDocForCurrency.id
    AND commission.btyp in (7, 8)
    AND ISNULL(commission.storno, 0) <> 1
    AND ISNULL(commission.proforma, 0) <> 1
LEFT OUTER JOIN
    [src_boss_entwicklung].[dbo].[devisen] AS currencies
    ON currencies.datum = (
            SELECT TOP 1 fc.datum
            FROM [src_boss_entwicklung].[dbo].[devisen] AS fc
            WHERE fc.datum <= originDocForCurrency.von
                AND fc.usd_brief IS NOT NULL AND fc.usd_brief > 0
                AND fc.usd_geld IS NOT NULL AND fc.usd_geld > 0
            ORDER BY fc.datum DESC
            )
WHERE
    originDocForCurrency.id = 68;