显示结果未加入 table

Question

我有三个 table：

child仁
活动
注册Activity

Table 'children' 包含 children.

的详细信息

Table 'activities' 包含 activity.

的详细信息

当 child 注册 activity 时，一个条目将添加到 table 中，其 activityID 和 childID。我正在尝试获取尚未注册 activity 的 children 的列表。我尝试了以下查询，但出现错误：

"Not unique table/alias: 'children'"

SELECT children.childrenEmailAddress
FROM children 
    INNER JOIN activities ON signupActivity.SignupActivityID = activities.activityID
    INNER JOIN children ON signupActivity.signupActivitychildID = children.childrenID
LEFT JOIN signupActivity ON children.childrenID = signupActivity.signupActivitychildID
WHERE activities.activityID = 8

记录集还需要包括基于在 table 中加入 'section' 的结果 Children 和 Activity。 children.childrenSection = activities.activitySection 以及按 activities.activityID

过滤记录集

这是我改编自 Arth 的决赛：

 SELECT c.childrenEmailAddress
     FROM children c
     JOIN activities a
       ON a.activitySection = c.childrenSection
        AND a.activityID = 8
LEFT JOIN signupActivity sa 
       ON sa.signupActivitychildID = c.childrenID
    WHERE sa.signupActivitychildID IS NULL

Answer 1

SELECT
    *
FROM
    Childeren C1
WHERE
    NOT EXISTS (SELECT *
        FROM
           signupActivity S1
        WHERE
           S1.activityID= 8 AND
           C1.ChildID= S1.ChildID)

Answer 2

我会使用 LEFT JOIN 和 NULL 检查

   SELECT c.childrenEmailAddress
     FROM children c
LEFT JOIN signupActivity sa 
       ON sa.signupActivitychildID = c.childrenID
      AND sa.SignupActivityID = 8
    WHERE sa.signupActivitychildID IS NULL

就我个人而言，我不喜欢在每个列名称中重复 table 名称。我发现使用它既没有必要又令人沮丧。您的查询可以很简单：

   SELECT c.emailAddress
     FROM child c
LEFT JOIN signupActivity sa 
       ON sa.childId = c.id 
      AND sa.activityID = 8
    WHERE sa.childId IS NULL

更新

   SELECT c.childrenEmailAddress
     FROM children c
     JOIN activities a
       ON a.activitySection = c.childrenSection
      AND a.activityID = 8
LEFT JOIN signupActivity sa 
       ON sa.signupActivitychildID = c.childrenID
      AND sa.signupActivityactivityID = a.activityID
    WHERE sa.signupActivitychildID IS NULL

Answer 3

SELECT *
FROM `children` c
WHERE c.childID NOT IN(
SELECT `childID`
FROM `activities`);

显示结果未加入 table

Show Results not in joining table

mysql

mysql-error-1064