GROUP BY 两列

Question

我想计算两列，但需要在一行中获取第一列的结果。

SELECT country, COUNT(*)
FROM table1
GROUP BY country, type

这个查询给了我

country    type     COUNT(*)
Canada     first    22
Canada     second   42
Canada     third    15
Australia  second   23
Australia  third    18

但我需要得到

country    type_first   type_second   type_third
Canada     22           42            15
Australia  23           18            0

因为我想用这些值更新另一个表，并且使用这个行结构，我可以根据上述查询逐行更新国家/地区表。

UPDATE country SET first=x, second=x, third=x

注意：type列ENUM具有预定义的值。

Answer 1

看起来你想要这样的东西：

SELECT country
, sum(case when type = 'first' then 1 else 0 end) as type_first
, sum(case when type = 'second' then 1 else 0 end) as type_second
, sum(case when type = 'third' then 1 else 0 end) as type_third
FROM table1
GROUP BY country