SQL 是否可以使用 COUNT 计算具有相同 ID 的所有行？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/30932283/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Is it possible to count all rows with the same id with COUNT?
提问by user3663882
PostgreSQL 9.4.
PostgreSQL 9.4.
I have the following table:
我有下表：
id player_id
serial PK integer
---------------------------
1 1
2 3
... ...
123123 1
I need to count all rows with player_id = 1. Is it possible to do with the COUNTaggregate?
我需要用player_id = 1. 可以用COUNT聚合吗？
Now I do it as follows:
现在我这样做：
SUM(CASE WHEN player_id = 1 THEN 1 ELSE 0 END)
回答by Elliot B.
If all you need is a count of the number of rows where player_idis 1, then you can do this:
如果您只需要计算行数player_id为 1，那么您可以执行以下操作：
SELECT count(*)
FROM your_table_name
WHERE player_id = 1;
If you want to count the number of rows for eachplayer_id, then you will need to use a GROUP BY:
如果要计算每个的行数player_id，则需要使用GROUP BY：
SELECT player_id, count(*)
FROM your_table_name
GROUP BY player_id;
