如何使用SQL将矩阵转换为可用表

Question

我正在努力将矩阵转换为可用的表，但是无法通过使用SQL并基本上重组整个文件的方式来提出创造性的方法

任何帮助/建议将不胜感激。

之前

     A       B       C       D
1   .5      .6      .7      .8      
2   .9      1.0     1.1     1.2
3   1.3     1.4     1.5     1.6
4   1.7     1.8     1.9     2.0

之后

X       Y       Result
A       1       .5
A       2       .9
A       3       1.3
A       4       1.7
.....

Answer 1

在MySQL中，最简单的方法可能是union all：

select 'A' as x, col1 as y, A as result from t union all
select 'B' as x, col1 as y, B as result from t union all
select 'C' as x, col1 as y, C as result from t union all
select 'D' as x, col1 as y, D as result from t;