如何改進包含子查詢的SELECT語句？

Question

我做了這個SELECT，但我認爲它可以改進。有誰知道如何才能讓它變得更好？

SELECT SUBSTRING_INDEX(acctEmail, '@', -1) as Domain, 
     (SELECT count(*) FROM accounts 
      WHERE acctType = 'A' AND SUBSTRING_INDEX(acctEmail, '@', -1) = Domain 
      GROUP BY SUBSTRING_INDEX(acctEmail, '@', -1) 
     ) as qtdAlias, 
     (SELECT count(*) FROM accounts 
      WHERE acctType = 'C' AND SUBSTRING_INDEX(acctEmail, '@', -1) = Domain 
      GROUP BY SUBSTRING_INDEX(acctEmail, '@', -1) 
     ) as qtdContas, 
     (SELECT count(*) FROM accounts 
      WHERE acctType = 'L' AND SUBSTRING_INDEX(acctEmail, '@', -1) = Domain 
      GROUP BY SUBSTRING_INDEX(acctEmail, '@', -1) 
     ) as qtdListas, 
     count(*) as Total 
FROM accounts 
GROUP BY Domain 
ORDER BY Total DESC; 

它帶來以下結果：

Answer 1

的一種方法是，使條件的總和爲

select 
substring_index(acctEmail, '@', -1) as Domain, 
sum(
case when acctType = 'A' then 1 else 0 end 
) as qtdAlias, 
sum(
case when acctType = 'C' then 1 else 0 end 
) as qtdContas, 
sum(
case when acctType = 'L' then 1 else 0 end 
) as qtdListas, 
count(*) as Total 
from accounts 
GROUP BY Domain 
ORDER BY Total DESC;