是否可以用COUNT计算具有相同ID的所有行？ [英] Is it possible to count all rows with the same id with COUNT?

问题描述

PostgreSQL 9.4 。

我有下表：

   id             player_id
serial PK          integer
---------------------------
   1                  1
   2                  3
  ...                ...
 123123               1

我需要计算 player_id = 1 的所有行。

I need to count all rows with player_id = 1. Is it possible to do with the COUNT aggregate?

现在可以按以下方式操作：

Now I do it as follows:

SUM(CASE WHEN player_id = 1 THEN 1 ELSE 0 END)

推荐答案

如果只需要计算 player_id 为1的行数，那么您可以执行以下操作：

If all you need is a count of the number of rows where player_id is 1, then you can do this:

SELECT count(*)
FROM your_table_name
WHERE player_id = 1;

如果要计算每个 <$ c的行数$ c> player_id ，那么您将需要使用 GROUP BY ：

If you want to count the number of rows for each player_id, then you will need to use a GROUP BY:

SELECT player_id, count(*)
FROM your_table_name
GROUP BY player_id;

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