Question

我有一个非空字段的表，我希望从另一个表填充。麻烦是查询到其他表可能会返回null。当查询返回null时，如何获取值（0将执行）？我的疑问是：

update Packages
    set PackageTypeId = (SELECT TOP 1 PackageTypeId
                         FROM PackageTypes
                         WHERE Packages.PackageTypeName = PackageTypes.Name
                         ORDER BY PackageTypeId ASC)

我尝试使用coalesce，但它仍然失败：

update Packages
     set PackageTypeId = (SELECT TOP 1 coalesce(PackageTypeId, 0) as id
                          FROM PackageTypes
                          WHERE Packages.PackageTypeName = PackageTypes.Name
                          ORDER BY PackageTypeId ASC)

有什么想法吗？

Answer 1

update Packages 
set PackageTypeId = coalesce((SELECT TOP 1 PackageTypeId FROM PackageTypes 
                              WHERE Packages.PackageTypeName = PackageTypes.Name 
                              ORDER BY PackageTypeId ASC), 0)

Answer 2

我建议将UPDATE FROM语句与ISNULL函数结合使用：

UPDATE
    Packages
SET
    Packages.PackageTypeId = ISNULL(PackageTypes.PackageTypeId,0)
FROM
    Packages
INNER JOIN
    (
        SELECT
            PackageTypeId,
            Name
        FROM
            (
                SELECT
                    PackageTypeId,
                    Name,
                    ROW_NUMBER() OVER (PARTITION BY Name ORDER BY PackageTypeId ASC) R
                FROM
                    PackageTypes
            ) X
        WHERE
            R = 1
    ) PackageTypes
ON
    Packages.PackageTypeName = PackageTypes.Name

注意：子查询为PackageType中的每个名称返回最小的PackageTypeId

如果select返回null，则使用默认值插入

2 个答案: