python - 将 Pandas 操作转换为 SQL 查询

Question

table = (df.groupby('name')['activity'].value_counts().unstack().fillna(0))

我有一个要创建的表，我可以在 python 中创建它，但我想在 sql 中创建它以获取它，如下所示:

activity tv football cooking chatting
name
chandler 0   0        3       2
monica   1   1        2       0
ross     3   2       1        1

我认为它应该是这样的，但我不能再进一步了。

SELECT name,
    COUNT(CASE WHEN END) AS ,
    COUNT(CASE WHEN END) AS
  FROM dataset
    GROUP BY name;

Answer 1

因此，您需要条件聚合:

SELECT name,
       SUM(CASE WHEN activity = 'tv' THEN 1 ELSE 0 END) AS tv,
       SUM(CASE WHEN activity = 'football' THEN 1 ELSE 0 END) AS football,
       SUM(CASE WHEN activity = 'cooking' THEN 1 ELSE 0 END) AS cooking,
       . . . 
FROM dataset
GROUP BY name;