如何在SQL Server

Question

添加三個表的屏幕截圖顯示了參考表。

我的目標是獲取每個國家最小 - 最大，平均工資日期

我想這個代碼

select 
    s.Descrip, 
    MIN(Salary) AS Minimum_per_state, 
    MAX(Salary) AS Maximum_per_state, 
    AVG(Salary) AS Average_per_state 
from 
    (select 
     Month_ending, 
     Emp_id,Salary, 
     Descrip 
    from 
     Dim_state 
    full join 
     Dim_city ON Dim_state.State_id = Dim_city.State_id 
    full join 
     Employee_details ON Dim_city.City_id = Employee_details.City_id 
    where 
     Month_ending = 20150131) s 
GROUP BY 
    Descrip 

，但我得到這樣的輸出：

description min_sal max_sal avg_sal 
Delhi  30000 34000 32000 
maharastra 25000 35000 30000 
tamil nadu 35000 50000 42000 
Westbengal 25000 50000 37500 

問題是班加羅爾和果阿丟失。

我可以知道哪部分出了問題嗎？

Answer 1

你有內部查詢的結果是什麼？

你可以直接嘗試這個（只使用左連接，並沒有使用內部查詢）？

SELECT ds.descip 
    ,min(salary) min_salary 
    ,max(salary) max_salary 
    ,avg(salary) avg_salary 
FROM dim_state ds 
LEFT JOIN dim_city dc ON ds.state_id = dc.state_id 
LEFT JOIN employee_details ed ON ed.city_id = dc.city_id 
WHERE Month_ending = 20150131 
GROUP BY ds.descip 

Answer 2

的，當你使用FULL，左或右連接聯接也很重要訂單。

SELECT ds.descip 
,min(salary) min_salary 
,max(salary) max_salary 
,avg(salary) avg_salary 
FROM employee_details ed 
     LEFT JOIN dim_city dc ON ed.city_id= dc.city_id 
     LEFT JOIN dim_state ed ON dc.state_id = dc.state_id 
      WHERE Month_ending = 20150131 
      GROUP BY ds.descip 

Answer 3

其實你錯過了一點。 dim_state有PK，這樣會在左側，而dim_city有FK，所以這將是在右側，以便使右連接

SELECT ds.descip 
,min(salary) min_salary 
,max(salary) max_salary 
,avg(salary) avg_salary 
FROM dim_state ds 
RIGHT JOIN dim_city dc ON ds.state_id = dc.state_id 
FULL JOIN employee_details ed ON ed.city_id = dc.city_id 
WHERE Month_ending = 20150131 
GROUP BY ds.descip