使用选择的联合构建MySQL视图

Question

我有一个包含以下结构的表： 列名称是指标（MT_NAME，MT_ADDRESS，MT_PHONE等），行是来自该发生的指标的值/得分（0,6,8,9,10）。 像这样：

+---------+------------+----------+
| MT_NAME | MT_ADDRESS | MT_PHONE |
+---------+------------+----------+
|       0 |          9 |        6 |
|       6 |         10 |        0 |
|       8 |         10 |        0 |
+---------+------------+----------+ 

我想构建一个包含3列的视图：一列具有表格列的名称，一列具有该列的不同值，另一列具有该列中出现的值的频率。 像这样：

+------------+----------+-------+
|   LEGEND   | CATEGORY | VALUE |
+------------+----------+-------+
| MT_NAME    |     0    |     1 |
| MT_NAME    |     6    |     1 |
| MT_NAME    |     8    |     1 |
| MT_ADDRESS |     9    |     1 |
| MT_ADDRESS |     10   |     2 |
| MT_PHONE   |     0    |     2 |
| MT_PHONE   |     6    |     1 |
+------------+----------+-------+

任何人都可以帮忙吗？

Answer 1

您可以使用union all：

select 'MT_NAME' as legend, mt_name as category, count(*) as frequency
from t
group by mt_name
union all
select 'MT_ADDRESS' as legend, mt_address as category, count(*) as frequency
from t
group by mt_name
union all
select 'MT_PHONE' as legend, mt_phone as category, count(*) as frequency
from t
group by mt_name;