SQL子查詢，從3行

Question

我有超過400萬行的龐大的數據庫，看起來像一個收集：

Customer ID Shop 
1   Asda 
1   Sainsbury 
1   Tesco 
2   TEsco 
2   Tesco 

我需要計算的客戶，過去4個星期內，在所有3個店樂購塞恩斯伯裏已經逛過和阿斯達。你可以請建議，如果它可能與子查詢做到這一點？

Answer 1

這是「set-set-sets」子查詢的一個示例。你可以用聚合來解決它：

select customer_id 
from Yourtable t 
where <shopping date within last four weeks> 
group by customer_id 
having sum(case when shop = 'Asda' then 1 else 0 end) > 0 and 
     sum(case when shop = 'Sainsbury' then 1 else 0 end) > 0 and 
     sum(case when shop = 'Tesco' then 1 else 0 end) > 0; 

這個結構非常靈活。所以，如果你想阿斯達和特易購，但不塞恩斯伯裏，那麼你會怎麼做：

select customer_id 
from Yourtable t 
where <shopping date within last four weeks> 
group by customer_id 
having sum(case when shop = 'Asda' then 1 else 0 end) > 0 and 
     sum(case when shop = 'Sainsbury' then 1 else 0 end) = 0 and 
     sum(case when shop = 'Tesco' then 1 else 0 end) > 0; 

編輯：

如果你想有一個數，然後用這個作爲一個子查詢和統計結果：

select count(*) 
from (select customer_id 
     from Yourtable t 
     where <shopping date within last four weeks> 
     group by customer_id 
     having sum(case when shop = 'Asda' then 1 else 0 end) > 0 and 
      sum(case when shop = 'Sainsbury' then 1 else 0 end) > 0 and 
      sum(case when shop = 'Tesco' then 1 else 0 end) > 0 
    ) t