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[英]get all rows from one table, sum on column from a second table using a where clause
[英]MySQL: How to select and display ALL rows from one table, and calculate the sum of a where clause on another table?
我正在嘗試顯示一個表中的所有行,並將結果SUM / AVG放在一列中,這是where子句的結果。 這可能沒什么意義,所以讓我解釋一下。
我需要顯示所有員工的報告......
SELECT Employees.Name, Employees.Extension
FROM Employees;
--------------
| Name | Ext |
--------------
| Joe | 123 |
| Jane | 124 |
| John | 125 |
--------------
...並加入來自PhoneCalls表的一些信息......
--------------------------------------------------------------
| PhoneCalls Table |
--------------------------------------------------------------
| Ext | StartTime | EndTime | Duration |
--------------------------------------------------------------
| 123 | 2010-09-05 10:54:22 | 2010-09-05 10:58:22 | 240 |
--------------------------------------------------------------
SELECT Employees.Name,
Employees.Extension,
Count(PhoneCalls.*) AS CallCount,
AVG(PhoneCalls.Duration) AS AverageCallTime,
SUM(PhoneCalls.Duration) AS TotalCallTime
FROM Employees
LEFT JOIN PhoneCalls ON Employees.Extension = PhoneCalls.Extension
GROUP BY Employees.Extension;
------------------------------------------------------------
| Name | Ext | CallCount | AverageCallTime | TotalCallTime |
------------------------------------------------------------
| Joe | 123 | 10 | 200 | 2000 |
| Jane | 124 | 20 | 250 | 5000 |
| John | 125 | 3 | 100 | 300 |
------------------------------------------------------------
現在我想過濾掉SUM和AVG計算中包含的一些行...
WHERE PhoneCalls.StartTime BETWEEN "2010-09-12 09:30:00" AND NOW()
...理想情況下會導致表格看起來像這樣:
------------------------------------------------------------
| Name | Ext | CallCount | AverageCallTime | TotalCallTime |
------------------------------------------------------------
| Joe | 123 | 5 | 200 | 1000 |
| Jane | 124 | 10 | 250 | 2500 |
| John | 125 | 0 | 0 | 0 |
------------------------------------------------------------
請注意,John沒有在此日期范圍內進行任何調用,因此他的總CallCount為零,但他仍然在結果列表中。 我似乎無法弄清楚如何在列表中保留像John這樣的記錄。 當我添加WHERE子句時,這些記錄被過濾掉。
如何創建一個顯示所有Employees的select語句,並且只顯示從WHERE子句返回的值的SUMs / AVG?
使用:
SELECT e.Name,
e.Extension,
Count(pc.*) AS CallCount,
AVG(pc.Duration) AS AverageCallTime,
SUM(pc.Duration) AS TotalCallTime
FROM Employees e
LEFT JOIN PhoneCalls pc ON pc.extension = e.extension
AND pc.StartTime BETWEEN "2010-09-12 09:30:00" AND NOW()
GROUP BY e.Name, e.Extension
問題是當使用OUTER JOIN時,在JOIN發生之前應用指定JOIN部分中的條件 - 就像派生表或內聯視圖一樣。 在OUTER JOIN之后應用WHERE
子句,這就是為什么當您在表上指定WHERE子句為LEFT OUTER JOIN時,您仍希望看到的行被過濾掉的原因。
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