使用mysql

Question

+--------------+  
| month | year |  
+-------+------+  
| jan   | 2015 |  
| jan   | 2015 |  
| jan   | 2015 |  
| feb   | 2015 |  
| feb   | 2015 |  
| feb   | 2015 |  
| feb   | 2015 |  
| feb   | 2015 |  
| mar   | 2015 |  
| mar   | 2015 |  
| mar   | 2015 |  
| mar   | 2015 |  
| mar   | 2015 |  
| mar   | 2015 |  
| mar   | 2015 |  
| mar   | 2016 |  
| mar   | 2016 |  
| mar   | 2016 |  
| mar   | 2016 |  
| mar   | 2016 |  
| mar   | 2016 |  
| mar   | 2016 |  
| mar   | 2016 |  
| feb   | 2016 |  
| feb   | 2016 |  
| jan   | 2016 |  
| jan   | 2016 |  
| jan   | 2016 |  
| jan   | 2016 |  
+--------------+

这是表格。

我需要每个月的平均率（即月/年）

Answer 1

您应该计算month列，而不是*。

以下是查询：

SELECT (COUNT(my.`month`)/(SELECT COUNT(*) FROM crate inmn WHERE inmn.`year` = my.`year`)) AS num, my.`month`, my.`year` FROM crate my GROUP BY my.`month`,my.`year;

以上查询的平均值为month，特别是year。