mysql - 将一列转置为mysql中的三个新列

Question

我在 mysql 中有一个表，其中包含以下列:

数据示例:

'16', '1', 'Evening', '6.00', '2014-06-05 08:14:35', '2014-06-04', '6.00'
'17', '2', 'Afternoon', '8.00', '2014-06-05 08:15:29', '2014-06-04', '8.00'
'18', '3', 'Afternoon', '4.00', '2014-06-05 08:17:32', '2014-06-04', '4.00'
'19', '4', 'Afternoon', '4.00', '2014-06-05 08:18:25', '2014-06-04', '4.00'
'20', '17', 'Morning', '2.00', '2014-06-05 09:11:40', '2014-06-05', '2.00'
'21', '17', 'Morning', '3.00', '2014-06-05 09:16:36', '2014-06-04', '3.00'
'22', '17', 'Evening', '2.00', '2014-06-05 09:17:43', '2014-06-04', '2.00'
'23', '19', 'Morning', '1.00', '2014-06-05 10:12:47', '2014-06-05', '1.00'
'24', '20', 'Morning', '2.00', '2014-06-05 10:16:02', '2014-06-05', '2.00'
'25', '22', 'Morning', '2.00', '2014-06-05 10:27:34', '2014-06-05', '2.00'
'26', '23', 'Morning', '2.00', '2014-06-05 10:28:08', '2014-06-05', '2.00'
'27', '24', 'Morning', '1.00', '2014-06-05 10:30:20', '2014-06-05', '1.00'
'28', '27', 'Morning', '1.00', '2014-06-05 10:43:12', '2014-06-05', '1.00'
'29', '27', 'Combined', '2.00', '2014-06-05 10:45:45', '2014-06-04', '2.00'
'31', '28', 'Morning', '3.00', '2014-06-05 11:04:32', '2014-06-05', '3.00'

我想转置时间列，这样我就有了晚上、下午和早上三个新列，并记录数量，使列看起来像
id、cow_id、Evening、Afternoon、Morning、date_added、date、quantity_type

有人可以给我一个关于如何使用 mysql 查询解决这个问题的解决方案吗？

Answer 1

如果你想在一行中包含给定日期的所有奶牛饲料，你可以尝试这样的事情:

SELECT cow_id, 
    SUM(CASE time WHEN 'Evening' THEN quantity ELSE 0 END) AS Evening,
    SUM(CASE time WHEN 'Afternoon' THEN quantity ELSE 0 END) AS Afternoon,
    SUM(CASE time WHEN 'Morning' THEN quantity ELSE 0 END) AS Morning,
    SUM(CASE time WHEN 'Combined' THEN quantity ELSE 0 END) AS Combined,
    `date`
FROM cows
GROUP BY cow_id, date

对于您的示例数据，这将给出如下结果(请注意，我必须为“合并”时间添加另一列):

cow_id  Evening Afternoon   Morning Combined    date    
1       6       0           0       0           2014-06-04  
2       0       8           0       0           2014-06-04  
3       0       4           0       0           2014-06-04  
4       0       4           0       0           2014-06-04  
17      2       0           3       0           2014-06-04  
17      0       0           2       0           2014-06-05  
19      0       0           1       0           2014-06-05  
20      0       0           2       0           2014-06-05  
22      0       0           2       0           2014-06-05  
23      0       0           2       0           2014-06-05  
27      0       0           0       2           2014-06-04  
27      0       0           1       0           2014-06-05  
28      0       0           3       0           2014-06-05