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[英]Selecting distinct count in a group with only null values for a specific column
[英]SQL query: selecting only NULL values from a group?
我正在使用看起来像这样的数据表:
Names City Date Color Shape
John Smith Baltimore 8/1/2015 Blue
John Smith Baltimore 8/1/2015 Green
John Smith Baltimore 8/1/2015 Rectangle
John Smith Baltimore 8/1/2015
John Smith Baltimore 8/1/2015 Square
John Smith Baltimore 8/1/2015
Rob Johnson Baltimore 8/1/2015
Rob Johnson Baltimore 8/1/2015
Rob Johnson Baltimore 8/1/2015
Rob Johnson Baltimore 8/1/2015
Rob Johnson Baltimore 8/1/2015
Greg Jackson Philadelphia 8/1/2015
Greg Jackson Philadelphia 8/1/2015
Greg Jackson Philadelphia 8/1/2015
Greg Jackson Philadelphia 8/1/2015 Circle
Greg Jackson Philadelphia 8/1/2015
Tom Green Philadelphia 8/1/2015
Tom Green Philadelphia 8/1/2015
Tom Green Philadelphia 8/1/2015 Red
Tom Green Philadelphia 8/1/2015
Tom Green Philadelphia 8/1/2015
我的查询目标是选择存在的所有五种数据类型,但隔离“名称”字段中在“颜色”和“形状”字段中具有NULL值的那些值。 我在MS Access中编写此SQL。 到目前为止,我的查询如下所示:
SELECT [Names], [City], [Date], [Color], [Shape]
FROM [databasename]
WHERE
(
([Color] IS NULL)
AND
([Shape] IS NULL)
);
从示例数据表中,我希望结果仅包括Rob Johnson,因为与该Name条目关联的所有行的Color和Shape字段均具有NULL值。 但是,通过此查询,我也获得了所有其他名称,并且返回了在Color和Shape字段中具有NULL值的特定行。
因此,预期的输出将如下所示:
Names City Date Color Shape
Rob Johnson Baltimore 8/1/2015
我怀疑我需要在此处使用GROUP运算符,但是我不确定如何执行此操作。 有任何想法吗?
我想你想要这个:
SELECT
DISTINCT [Names], [City], [Date], [Color], [Shape]
FROM [table]
WHERE [Names] NOT IN (
SELECT [Names] FROM [table] WHERE ([Color] IS NOT NULL) OR
([Shape] IS NOT NULL)
);
可以用其他方式完成此操作,但这应该与您的原始查询接近。
您可以使用聚合和内部联接:
SELECT d1.* FROM [database-name] d1
INNER JOIN (
select Names,MAX(Color) as mc,MAX(Shape) as ms
from [database-name]
group by Names
) d2
ON d1.Names = d2.Names
WHERE mc IS NULL
AND ms IS NULL
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