SQL重複電話查詢

Question

我有兩個電話號碼錶，我想運行查詢來檢查兩個表中是否有重複的電話號碼。該表被稱爲1類和我CLASS2想出了以下查詢：

Select * 
from Class1 
where Telephone in (select 
       Telephone 
       from Class2 
       group by Telephone 
       having count(*) > 1) 

它不工作，任何人可以幫我嗎？

Answer 1

你混合兩件事情：

Select * from Class1 where Telephone in (select Telephone from Class2); 

爲您提供了存在兩個表中的所有數字。

Select Telephone from Class1 group by Telephone having count(*) > 1; 

爲您提供Class1中的所有重複數字。

您可以結合這些：

Select 'Class1' as whattable, Telephone from Class1 group by Telephone having count(*) > 1 
union all 
Select 'Class2' as whattable, Telephone from Class2 group by Telephone having count(*) > 1 
union all 
Select 'both' as whattable, Telephone from Class1 where Telephone in (select Telephone from Class2);