mysql子查询返回多行查询错误

我有许多用于消息传递系统的表。但我无法将查询发送到mysql

SELECT 
            messages_list.IDUSER,
            messages_list.IDPAGE,
            messages_list.IDUSER,
            messages_list.v_readed,
            messages_list.IDUSER,
            messages_texts.v_text,
            messages_texts.v_time,
            messages_subjects.v_title,
            user_photos.v_photoURL,
            user.v_sex,
            (SELECT IDPHOTO FROM user WHERE messages_list.IDUSER)
        FROM 
            messages_texts,
            user
        INNER JOIN user_photos ON user_photos.ID=user.IDPHOTO AND user_photos.v_active='1' 
        INNER JOIN messages_list ON messages_list.IDUSER=717306 AND messages_list.v_active='1'
        INNER JOIN messages_subjects ON messages_list.IDSUBJECT=messages_subjects.ID
        INNER JOIN messages_users ON messages_users.IDSUBJECT=messages_subjects.ID AND messages_users.IDUSER=user.ID
        WHERE
            messages_users.IDUSER<>717306  
        GROUP BY messages_subjects.ID
        ORDER BY messages_list.ID
    )\n: (Subquery returns more than 1 row)

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问题出在哪里？？？

相关子查询不能返回多行。此查询：

SELECT IDPHOTO FROM user WHERE messages_list.IDUSER

返回多个它无法执行的行。您需要使用limit子句将其限制为仅一行：

或者使用特定的键：

SELECT IDPHOTO FROM user WHERE messages_list.IDUSER WHERE id=1

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问题在于此子查询：

        (SELECT IDPHOTO FROM user WHERE messages_list.IDUSER)

它嵌套在select语句中，因此它应该只返回一个值。where子句只包含IDUSER值。假设该字段为整数，则只要该值不是0，就会返回true。所以，它基本上会返回所有用户

您可能希望为特定用户创建一个/IDPHOTO：

        (SELECT IDPHOTO FROM user WHERE messages_list.IDUSER = user.ID)

        (SELECT IDPHOTO FROM user WHERE messages_list.IDUSER = user.ID)