獲取n個組的所有記錄

Question

我有一個表有多個路徑的共享我想要獲取所有路徑，其中這些路徑中的前N個不同Servername作爲示例在這裏整個表。

+----+--------------------------------+ 
| ID | BACKUPPATH      | 
+----+--------------------------------+ 
| 1 | //server.domain/share/folder | 
| 2 | //server.domain/share/folder3 | 
| 3 | //server.domain/share/folder2 | 
| 4 | //server2.domain/share/folder1 | 
| 5 | //server2.domain/share/folder2 | 
| 6 | //server3.domain/share/folder1 | 
| 7 | //server3.domain/share/folder2 | 
| 8 | //server3.domain/share/folder3 | 
+----+--------------------------------+ 

服務器名稱可能會有所不同，每個不同的Servenames可能會有所不同。作爲例子，我希望得到我期望的那樣結果前2個不同servernames節點的所有路徑：

+----+--------------------------------+ 
| ID | BACKUPPATH      | 
+----+--------------------------------+ 
| 1 | //server.domain/share/folder | 
| 2 | //server.domain/share/folder3 | 
| 3 | //server.domain/share/folder2 | 
| 4 | //server2.domain/share/folder1 | 
| 5 | //server2.domain/share/folder2 | 
+----+--------------------------------+ 

爲子查詢我用下面的查詢來獲取servernames節點的行集：

select SUBSTRING_INDEX(BACKUPPATH,'/',3) as SERVERNAMES from(select BACKUPPATH from Backuppaths GROUP BY SUBSTRING_INDEX(BACKUPPATH,'/',3))as NUMEROFSERVERS LIMIT 2; 

+------------------+ 
| SERVERNAMES  | 
+------------------+ 
| //server.domain | 
| //server2.domain | 
+------------------+ 

我被困現在在如何使用這個子查詢來獲得我期望的結果。

感謝在這個

Answer 1

任何幫助，您可以加入到聯視圖：

select s.* 
    from servernames s 
    join (select substring_index(backuppath, '/', 3) as servername 
      from servernames 
     group by servername 
     order by min(id) limit 2) v 
    on substring_index(backuppath, '/', 3) = v.servername 
order by id 

Fiddle:http://sqlfiddle.com/#!2/b6a16/1/0

Answer 2

使用Distinct

SELECT DISTINCT SUBSTRING_INDEX(BACKUPPATH,'/',3) AS SERVERNAMES FROM Backuppaths LIMIT 2;