[英]Selecting column pairs where one of the columns occurs in at least two distinct pairs
我希望從MySQL表中選擇一對不同的值,其中一列的值至少出現兩次。
例如,我有下表:
+----+---------+----------+-----------+
| id | machine | filename | ipaddress |
+----+---------+----------+-----------+
| 1 | X | /tmp/1 | 1.2.3.4 |
| 2 | X | /tmp/2 | 1.2.3.4 |
| 3 | X | /tmp/3 | 2.3.4.5 |
| 4 | Y | /tmp/4 | 2.3.4.5 |
| 5 | Z | /tmp/5 | 2.3.4.5 |
| 6 | Z | /tmp/6 | 2.3.4.5 |
+----+---------+----------+-----------+
我希望選擇至少兩台machine
存在特定ipaddress
所有行。 只需要一machine
ipaddress
-pair,因此結果將是:
+---------+-----------+
| machine | ipaddress |
+---------+-----------+
| X | 2.3.4.5 |
| Y | 2.3.4.5 |
| Z | 2.3.4.5 |
+---------+-----------+
我嘗試在機器和ipaddress上分組:
SELECT machine, ipaddress FROM table
GROUP BY machine, ipaddress HAVING count(*) > 1
但是,這也導致包含(X,1.2.3.4)。
我也嘗試使用子查詢,但這僅返回任何ipaddress一次:
SELECT machine, ipaddress FROM
(SELECT machine, ipaddress FROM table GROUP BY machine, ipaddress) t
GROUP BY ipaddress HAVING count(*) > 1
我很難找到正確的查詢。 應當注意,該表相當大,並且在某種程度上需要有效的查詢。
目前我還沒有MySQL,但是我在SQL Server中嘗試了以下操作,它似乎可以解決您的問題。 確保編寫一些單元測試來驗證:
SELECT DISTINCT machine, ipaddress
FROM [table] t1
WHERE EXISTS (
SELECT 1
FROM [table] t2
WHERE t1.ipaddress = t2.ipaddress
GROUP BY ipaddress
HAVING COUNT(DISTINCT machine) > 1);
這將產生您的數據:
+---------+-----------+
| machine | ipaddress |
+---------+-----------+
| X | 2.3.4.5 |
| Y | 2.3.4.5 |
| Z | 2.3.4.5 |
+---------+-----------+
此替代語法也可以使用,並且對於MySQL可能(或可能不)更快(如果對您很重要,請進行性能測試):
SELECT DISTINCT machine, ipaddress
FROM [table]
WHERE ipaddress IN (
SELECT ipaddress
FROM [table]
GROUP BY ipaddress
HAVING COUNT(DISTINCT machine) > 1);
試試這個:
SELECT machine, ipaddress FROM
(SELECT DISTINCT machine, ipaddress FROM table) t
GROUP BY ipaddress,machine HAVING count(*) > 1
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