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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?
我正在使用看起來像這樣的數據表:
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
我的查詢目標是選擇存在的所有五種數據類型,但隔離“名稱”字段中在“顏色”和“形狀”字段中具有NULL值的那些值。 我在MS Access中編寫此SQL。 到目前為止,我的查詢如下所示:
SELECT [Names], [City], [Date], [Color], [Shape]
FROM [databasename]
WHERE
(
([Color] IS NULL)
AND
([Shape] IS NULL)
);
從示例數據表中,我希望結果僅包括Rob Johnson,因為與該Name條目關聯的所有行的Color和Shape字段均具有NULL值。 但是,通過此查詢,我也獲得了所有其他名稱,並且返回了在Color和Shape字段中具有NULL值的特定行。
因此,預期的輸出將如下所示:
Names City Date Color Shape
Rob Johnson Baltimore 8/1/2015
我懷疑我需要在此處使用GROUP運算符,但是我不確定如何執行此操作。 有任何想法嗎?
我想你想要這個:
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,但這應該與您的原始查詢接近。
您可以使用聚合和內部聯接:
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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