基于映射表显示结果

Question

我有两个mysql表，第一个表Activity将病人活动级别存储为整数，另一个表用描述映射每个整数。我正在尝试创建一个select查询，为我提供对病人活动的描述，而不是整数值。

Activity Table
id|pid|bathing|cognition|housekeeping|dressing|feeding|meal
1 | 20|  4    |   4     |      2     |    6   |   8   |   4
2 | 40|  4    |   2     |      4     |    4   |   6   |   6  

Mapping Table
value|description
2    | Independent
4    | Minimal 
6    | Moderate
8    | Maximum

Desired Query Result

id|cid|bathing|cognition|housekeeping|dressing|feeding|meal
1 | 20|Minimal|Minimal  |Independent |Moderate|Maximum|Minimal

我已经研究过使用mysql的情况，但这似乎不起作用。我还回顾了这两个堆叠溢出问题-- Question1和Questions2 --它们似乎并不是我想要的。

Answer 1

下面的代码使用映射表显示正确的描述。关于选择子查询的MYSQL文档。

Select id, pid,
(Select description from mapping where value=a.bathing) as 'bathing',
(Select description from mapping where value=a.cognition) as 'cognition',
(Select description from mapping where value=a.housekeeping) as 'housekeeping',
(Select description from mapping where value=a.dressing) as 'dressing',
(Select description from mapping where value=a.feeding) as 'feeding',
(Select description from mapping where value=a.meal) as 'meal'
From activity a

Answer 2

另一种使用左联接的方法：

select 
  id, 
  pid, 
  m1.description as bathing,
  m2.description as cognition,
  m3.description as housekeeping,
  m4.description as dressing,
  m5.description as feeding,
  m6.description as meal
from activity
left join mapping m1 on m1.value = bathing
left join mapping m2 on m2.value = cognition 
left join mapping m3 on m3.value = housekeeping 
left join mapping m4 on m4.value = dressing 
left join mapping m5 on m5.value = feeding 
left join mapping m6 on m6.value = meal 

示例SQL Fiddle

使用MySQL，对于每个要映射值的列，可能都无法绕过加入映射表一次。(在MSSQL上，您可以使用unpivot/pivot (示例))。