SQL子查询返回多个结果

Question

我有一个查询，当我检查，如果过滤器是NULL，则我选择所有，但如果它们不为空，我只选择具有这些过滤器的对象。查询如下。

SELECT * 
FROM [PointOfInterest]
WHERE [PointOfInterest].[Id] IN (CASE
                                    WHEN @filters IS NULL THEN [PointOfInterest].[Id]
                                    WHEN @filters IS NOT NULL THEN (SELECT DISTINCT [PointOfInterestIcon].[PointOfInterestId]
                                            FROM  [PointOfInterestIcon]
                                            WHERE [IconId] IN (SELECT [Id] FROM OPENJSON(@filters)WITH([Id] NVARCHAR(255))))
                                    END)

如果我删除CASE语句，把只有SELECT的查询工作。任何想法如何解决这一问题？

Answer 1

只要使用正规布尔逻辑：

SELECT * 
FROM [PointOfInterest]
WHERE @filters IS NULL OR
      [PointOfInterest].[Id] IN (SELECT poi.[PointOfInterestId]
                                 FROM [PointOfInterestIcon] poi
                                 WHERE poiIconId IN (SELECT [Id] FROM OPENJSON(@filters) WITH ([Id] NVARCHAR(255)))
                                );

Answer 2

你有一个内部的选择是不是行返回更多..你可以使用TOP 1的上限这一结果

SELECT * 
FROM [PointOfInterest]
WHERE [PointOfInterest].[Id] IN (
    CASE
            WHEN @filters IS NULL THEN [PointOfInterest].[Id]
            WHEN @filters IS NOT NULL THEN (
                    SELECT TOP 1 DISTINCT [PointOfInterestIcon].[PointOfInterestId]
                    FROM  [PointOfInterestIcon]
                    WHERE [IconId] IN (
                    SELECT [Id] FROM OPENJSON(@filters)WITH([Id] NVARCHAR(255))))
    END)