Postgres得到计数但是由另一列分组

Question

如果我有一张像这样的桌子

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

我如何计算总喜欢但按客户分组，所以我最终得到的结果如下：

customer total_likes
1        2
2        1
3        1

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，请执行以下操作：

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

SELECT CUSTOMER, COUNT(LIKED) AS TOTAL_LIKES
FROM TABLE
WHERE LIKED = 'true'
GROUP BY CUSTOMER

Answer 4

我假设liked是一个布尔类型字段，

SELECT customer, COUNT(liked) AS total_likes
FROM table_name 
WHERE liked is true
GROUP BY customer

Answer 5

在COUNT函数内使用CASE语句。

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