Mysql按年份和計數分組字段

Question

例如，我有一個這樣的表：

|  id  |  name  |  register_date  |  gender  |

|1     |John    |2011-02-02       |man       |
|2     |Jane    |2011-02-02       |woman     |
|3     |Jihn    |2012-04-04       |man       |
|4     |Jeni    |2012-02-02       |woman     |
|5     |Joni    |2012-02-02       |woman     |

如何從上面的表中查詢創建此結果的查詢？

|  RegisterYear  |  man  |  woman  |

|2011            |   1   |    1    |
|2012            |   1   |    2    |

Answer 1

按年份分組並匯總每個性別

select year(register_date) as registeryear,
       sum(gender = 'man') as man,
       sum(gender = 'woman') as woman       
from your_table
group by registeryear

Answer 2

干得好：

SELECT YEAR(register_date) as RegisterYear,
       SUM(gender = 'man') as man,
       SUM(gender = 'woman') as woman
from register 
group by RegisterYear;

SQLFiddle演示

輸出：

REGISTERYEAR    MAN     WOMAN
===================================
2011            1       1
2012            1       2