Postgres得到計數但是由另一列分組

Question

如果我有一張像這樣的桌子

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

我如何計算總喜歡但按客戶分組，所以我最終得到的結果如下：

customer total_likes
1        2
2        1
3        1

Answer 1

GROUP BY和條件COUNT應該：

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

如果它是布爾列，請執行以下操作：

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

Answer 2

在Postgres中，您可以使用簡寫從布爾值轉換為整數：

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

請注意，這將返回所有客戶 ，而不僅僅是那些喜歡的客戶 。 如果您只想要喜歡的客戶，那么where子句是合適的：

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

我假設liked是一個布爾類型字段，

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

Answer 5

在COUNT函數內使用CASE語句。

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