变换表热编码一个单独列的值的

Question

我有两列的表：

+---------+--------+ 
| keyword | color | 
+---------+--------+ 
| foo  | red | 
| bar  | yellow | 
| fobar | red | 
| baz  | blue | 
| bazbaz | green | 
+---------+--------+ 

我需要做某种独热编码和PostgreSQL的转换表：

+---------+-----+--------+-------+------+ 
| keyword | red | yellow | green | blue | 
+---------+-----+--------+-------+------+ 
| foo  | 1 |  0 |  0 | 0 | 
| bar  | 0 |  1 |  0 | 0 | 
| fobar | 1 |  0 |  0 | 0 | 
| baz  | 0 |  0 |  0 | 1 | 
| bazbaz | 0 |  0 |  1 | 0 | 
+---------+-----+--------+-------+------+ 

是否可以只使用SQL？有关如何开始的任何提示？

Answer 1

如果我理解正确的，你需要有条件聚集：

select keyword, 
count(case when color = 'red' then 1 end) as red, 
count(case when color = 'yellow' then 1 end) as yellow 
-- another colors here 
from t 
group by keyword