Mysql 简单的SQL连接查询（我想）

有人能告诉我为什么我在使用完全联接时，在“where子句”中出现错误：未知列“cdu\u user\u progress.uid”，但在仅使用联接时却没有？我正在使用MySQL

SELECT 
    cdu_lessons.*, 
    SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 0 THEN score END ORDER BY date), ',', 1) AS game0_first,
    MAX(CASE WHEN game_id = 0 THEN score END) AS game0_max,
    SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 1 THEN score END ORDER BY date), ',', 1) AS game1_first,
    MAX(CASE WHEN game_id = 1 THEN score END) AS game1_max,
    SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 2 THEN score END ORDER BY date), ',', 1) AS game2_first,
    MAX(CASE WHEN game_id = 2 THEN score END) AS game2_max,
    SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 3 THEN score END ORDER BY date), ',', 1) AS game3_first,
    MAX(CASE WHEN game_id = 3 THEN score END) AS game3_max,
    SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 4 THEN score END ORDER BY date), ',', 1) AS game4_first,
    MAX(CASE WHEN game_id = 4 THEN score END) AS game4_max,
    SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 5 THEN score END ORDER BY date), ',', 1) AS game5_first,
    MAX(CASE WHEN game_id = 5 THEN score END) AS game5_max     
FROM cdu_user_progress 
FULL JOIN cdu_lessons ON cdu_lessons.id = cdu_user_progress.lesson_id 
WHERE cdu_user_progress.uid = 145 
GROUP BY lesson_id

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MySQL缺乏对完全外部连接的支持

因此，如果您想在MySQL上模拟完全连接，请看一看

通常建议的解决方法如下所示：

   SELECT 
        cdu_lessons.*, 
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 0 THEN score END ORDER BY date), ',', 1) AS game0_first,
        MAX(CASE WHEN game_id = 0 THEN score END) AS game0_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 1 THEN score END ORDER BY date), ',', 1) AS game1_first,
        MAX(CASE WHEN game_id = 1 THEN score END) AS game1_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 2 THEN score END ORDER BY date), ',', 1) AS game2_first,
        MAX(CASE WHEN game_id = 2 THEN score END) AS game2_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 3 THEN score END ORDER BY date), ',', 1) AS game3_first,
        MAX(CASE WHEN game_id = 3 THEN score END) AS game3_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 4 THEN score END ORDER BY date), ',', 1) AS game4_first,
        MAX(CASE WHEN game_id = 4 THEN score END) AS game4_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 5 THEN score END ORDER BY date), ',', 1) AS game5_first,
        MAX(CASE WHEN game_id = 5 THEN score END) AS game5_max     
    FROM cdu_user_progress 
    LEFT JOIN cdu_lessons ON cdu_lessons.id = cdu_user_progress.lesson_id 
    WHERE cdu_user_progress.uid = 145 
    GROUP BY lesson_id

Union ALL

    SELECT 
        cdu_lessons.*, 
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 0 THEN score END ORDER BY date), ',', 1) AS game0_first,
        MAX(CASE WHEN game_id = 0 THEN score END) AS game0_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 1 THEN score END ORDER BY date), ',', 1) AS game1_first,
        MAX(CASE WHEN game_id = 1 THEN score END) AS game1_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 2 THEN score END ORDER BY date), ',', 1) AS game2_first,
        MAX(CASE WHEN game_id = 2 THEN score END) AS game2_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 3 THEN score END ORDER BY date), ',', 1) AS game3_first,
        MAX(CASE WHEN game_id = 3 THEN score END) AS game3_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 4 THEN score END ORDER BY date), ',', 1) AS game4_first,
        MAX(CASE WHEN game_id = 4 THEN score END) AS game4_max,
        SUBSTRING_INDEX(GROUP_CONCAT(CASE WHEN game_id = 5 THEN score END ORDER BY date), ',', 1) AS game5_first,
        MAX(CASE WHEN game_id = 5 THEN score END) AS game5_max     
    FROM cdu_user_progress 
    RIGHT JOIN cdu_lessons ON cdu_lessons.id = cdu_user_progress.lesson_id 
    WHERE cdu_user_progress.uid = 145 
    GROUP BY lesson_id

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mysql中不支持

完全连接

，至少不支持直接从cdu\u user\u progress进行

完全连接…

被解释为来自cdu的

\u用户\u进度为完全

。 本质上，它用别名FULL替换表名