Postgres得到计数但是由另一列分组

Question

如果我有一张像

这样的表格

recognizer.setKeywordThreshold(1e-40f)

我如何计算总体喜欢但按客户分组，所以我最终得到的结果如下：

customer liked
1        true
2        true
3        true
1        true
2        false

Answer 1

GROUP BY和条件COUNT应该：

SELECT customer, COUNT(CASE WHEN liked = 'true' THEN 1 END) AS likes
FROM yourtable
group by customer

如果它是布尔列，请执行：

SELECT customer, COUNT(CASE WHEN liked THEN 1 END) AS likes
FROM yourtable
group by customer

Answer 2

在Postgres中，您可以使用简写从布尔值转换为整数：

select customer, sum(liked::int) as total_likes
from t
group by customer;

请注意，这将返回所有客户，而不仅仅是那些喜欢的客户。如果您只想要喜欢的客户，那么where子句是合适的：

select customer, count(*)
from t
where liked
group by customer;

Answer 3

ng-class="{className:[condition]}"

ng-class="{custom-directive:[value =='ABC']}"

Answer 4

我假设SELECT customer, COUNT(liked) AS total_likes FROM table_name WHERE liked is true GROUP BY customer 是一个布尔类型字段，

ids = @anonymous.ids
ids.concat(@amitian.ids) if amitian_signed_in?
@confessions = Confession.where(amitian_id: ids).order('created_at DESC')

Answer 5

在CASE函数中使用COUNT语句。

SELECT customer, COUNT(CASE WHEN liked = 'true' THEN 1 ELSE NULL END) AS total_likes
FROM yourtable