SQL Query在有重复项时选择一个集合

Question

SELECT REF_ID, MIN(SLA) FROM [SLA] WHERE [FIRST_DATE] > '2016-09-30' GROUP BY  [REF_ID]  

当存在重复时，这将列出具有最小SLA的项目

REF_ID    |    COUNT  
11    |    1  
12    |    1  
13    |    1  
14    |    2  

我想获得SLA的数量，有人可以为此提供查询。

SLA    |    COUNT  
1    |    3  
2    |    1  
0    |    0  

由于

Answer 1

获取SLA的数量：

select SLA, count(SLA) from table group by SLA

Answer 2

试试这个

SELECT MINSLA, COUNT(MINSLA)
FROM (SELECT REF_ID, MIN(SLA) AS MINSLA
      FROM [SLA]
      WHERE [FIRST_DATE] > '2016-09-30'
      GROUP BY [REF_ID]
     ) r
GROUP BY MINSLA