如何優化內連接

Question

我有兩個表格。 They are in Heidi 我需要表所示：Rezult

我嘗試下一個選擇：

SELECT accounts.name, accounts.account_id,date, 
    (case when accounts.account_id = results.account_id then date end) AS Dat, 
results.account_id 
FROM results 
INNER JOIN accounts 
group by date,dat,name 
order by accounts.account_id ,date 

但我不需要的字段。幫助擺脫他們。

此外： 我必須證明表是這樣的：

--------------------01.2010----02.2010-----03.2010---nextDate 

Revenues ----------'x'------------'x'---------'null'--------------------- 

Personal Costs-----'x'------------'x'---------'x'--------------------- 

Amortisation---------'x'------------'x'---------'null'--------------------- 

Summa---------------'3x'-----------'3x'---------'1x'--------------------- 

我用下一個選擇：

SELECT 
GROUP_CONCAT(revenues SEPARATOR ';')as Renenues, 
GROUP_CONCAT(personal SEPARATOR ';')as Personal, 
GROUP_CONCAT(amortisation SEPARATOR ';')as Amortisation 
from (SELECT date, 
sum(case when accounts.account_id = 1 then 1 else 0 end) as revenues, 
sum(case when accounts.account_id = 2 then 1 else 0 end) as personal , 
sum(case when accounts.account_id = 3 then 1 else 0 end) as amortisation 
from accounts 
left JOIN results on accounts.account_id = results.account_id 
group by date 
) t 
UNION ALL 
SELECT 
sum(case when results.account_id = 1 then 1 ELSE 0 end) , 
sum(case when results.account_id = 2 then 1 else 0 end) , 
sum(case when results.account_id = 3 then 1 else 0 end) 
from results 

然後，我將展示錶行從我的字符串： 'GROUP_CONCAT'。 可能使這樣的SELECT不知道'accounts.account_id'的數量或優化這個SELECT？ 我嘗試了第一個SELECT，但得到了很多不必要的信息。

Answer 1

您應修改您的查詢要像

SELECT accounts.name, 
accounts.account_id as accounts_account_id, 
accounts.date, 
results.account_id as results_account_id 
FROM results 
LEFT JOIN accounts ON accounts.account_id = results.account_id 
group by accounts.date,accounts.name 
order by accounts.account_id ,accounts.date;