SQL 查询对多列中的条目进行计数

Question

我有一个包含两个表的数据库:tblPlayers 和 tblMatches。

tblPlayers 包含以下字段:playerID、playerName。

tblMatches 包含 matchID、scorer1ID、scorer2ID、scorer3ID。

我需要运行一个查询来计算一名球员的进球总数，并返回其球员 ID。

我尝试了以下方法:

SELECT
tblPlayers.playerID, tblPlayers.playerName, count(*) AS goals
FROM
tblPlayers, matches
WHERE
(tblPlayers.playerID = tblMatches.scorer1ID
OR
tblPlayers.playerID = tblMatches.scorer2ID
OR
tblPlayers.playerID = tblMatches.goalscorer3ID)
GROUP BY tblPlayers.playerID
ORDER BY goals DESC

但是，这并不能按要求工作，因为计数函数不允许球员在一场比赛中进球超过一个进球(例如，如果球员进球三个进球，他的 ID 会出现在 Scorer1ID 中)字段、scorer2ID 字段和 Scorer3ID 字段，但计数只返回值 1，而当需要为 3 时)。

希望这是有道理的，过去几天我一直在努力解决这个问题!非常感谢任何帮助。

Answer 1

SELECT
    playerID,
    playerName,
    SUM(goals) AS goals
FROM 
(
    SELECT p.playerID, p.playerName, COUNT(*) AS goals
    FROM 
        tblPlayers p
        JOIN tblMatches m ON m.scorer1ID = p.playerID
    GROUP BY p.playerID, p.playerName

    UNION ALL

    SELECT p.playerID, p.playerName, COUNT(*) AS goals
    FROM 
        tblPlayers p
        JOIN tblMatches m ON m.scorer2ID = p.playerID
    GROUP BY p.playerID, p.playerName

    UNION ALL

    SELECT p.playerID, p.playerName, COUNT(*) AS goals
    FROM 
        tblPlayers p
        JOIN tblMatches m ON m.scorer3ID = p.playerID
    GROUP BY p.playerID, p.playerName
) sub
GROUP BY playerID, playerName

或者，这里有一个一次性执行此操作的查询:

SELECT 
    p.playerID, 
    p.playerName, 
    SUM (
        CASE WHEN p.playerID = m.scorer1ID THEN 1 ELSE 0 END +
        CASE WHEN p.playerID = m.scorer2ID THEN 1 ELSE 0 END +
        CASE WHEN p.playerID = m.scorer3ID THEN 1 ELSE 0 END
    ) AS goals
FROM 
    tblPlayers p
    JOIN tblMatches m ON p.playerID IN (m.scorer1ID, m.scorer2ID, m.scorer3ID)
GROUP BY p.playerID, p.playerName