SQL Server:在选择中显示NULL的默认值

我有一个存储过程，它根据一些选择创建XML字符串

如果其中一个select返回NULL，是否有一种方法可以显示默认值？ 基本上，我只想在XML中保持相同的结构，与值是否为NULL无关。当前，XML仅显示带有值的记录

存储过程示例：

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非常感谢你在这方面的帮助，蒂姆

试试这样的东西

SELECT      coalesce(A.ranking,0) as ranking
            (
                SELECT      coalesce(B.groupName,'') as groupName,
                            (
                                SELECT      C.policy,
                                            C.groupCount
                                FROM        @temp C
                                WHERE       C.ranking = A.ranking
                                AND         C.groupName = B.groupName
                                ORDER BY    C.groupCount desc, C.policy
                                FOR XML PATH(''), ELEMENTS, TYPE
                            ) AS groupName
                FROM        @temp B
                WHERE       B.ranking = A.ranking
                GROUP BY    B.groupName
                ORDER BY    B.groupName
                FOR XML PATH(''), ELEMENTS, TYPE
            )
FROM        @temp A
GROUP BY    A.ranking
ORDER BY    A.ranking
FOR XML PATH('policyRanking'), ELEMENTS, TYPE, ROOT('ranks')

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试试这样的

SELECT      coalesce(A.ranking,0) as ranking
            (
                SELECT      coalesce(B.groupName,'') as groupName,
                            (
                                SELECT      C.policy,
                                            C.groupCount
                                FROM        @temp C
                                WHERE       C.ranking = A.ranking
                                AND         C.groupName = B.groupName
                                ORDER BY    C.groupCount desc, C.policy
                                FOR XML PATH(''), ELEMENTS, TYPE
                            ) AS groupName
                FROM        @temp B
                WHERE       B.ranking = A.ranking
                GROUP BY    B.groupName
                ORDER BY    B.groupName
                FOR XML PATH(''), ELEMENTS, TYPE
            )
FROM        @temp A
GROUP BY    A.ranking
ORDER BY    A.ranking
FOR XML PATH('policyRanking'), ELEMENTS, TYPE, ROOT('ranks')

使用函数，将每个可为空的列替换为表达式see table definition：

 ISNULL ( column , default_value )

使用函数，将每个可为空的列替换为表达式see table definition：

 ISNULL ( column , default_value )

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谢谢您能解释一下coalesce在这里做什么吗？如果列为NullThank，则coalesce将设置作为第二个参数输入的值！您能解释一下coalesce在这里做什么吗？如果列为NULL，则coalesce将设置作为第二个参数输入的值