问题理解内部连接或左连接

Question

我在理解内连接和左连接时遇到问题

我在外部系统中有以下查询

 SELECT {CLD}.[Id], {CLD}.[Name], {CLD}.[Comments]
      , {CLD}.[LastUpdateOn],min({Project}.[Number])
      ,count({Project}.[Number])
 FROM {CLD}
     INNER JOIN {Project} ON  {Project}.[Id] = {CLDProjects}.[ProjectId] 
     INNER JOIN {CLDProjects} ON {CLD}.[Id] = {CLDProjects}.[CLDId]
 WHERE 
   (
     @IsJAXPM =1 
     or EXISTS (SELECT 1 
             FROM {CLDParticipant} 
             WHERE {CLDParticipant}.[CLDId] = {CLD}.[Id] 
               AND {CLDParticipant}.[UserId] = @UserId) 
     or EXISTS (SELECT 1 
                FROM {ProjectParticipantWidget} 
                    INNER JOIN {ProjectParticipant} ON {ProjectParticipantWidget}.[ProjectParticipantId] =  {ProjectParticipant}.[Id]
                WHERE {ProjectParticipant}.[ProjectId] = {Project}.[Id] 
                  AND {ProjectParticipant}.[UserId] = @UserId)
   )
 GROUP BY {CLD}.[Id], {CLD}.[Name], {CLD}.[Comments], {CLD}.[LastUpdateOn]

问题是 Select 在不考虑项目的情况下拉取所有 CLD 元素，我正在尝试 select CLD 的项目 ID = Project.Id。我尝试了两种连接，但它一直在提取所有值下面是结构的样子

Answer 1

请尝试以下操作：首先获取与 Project 匹配的 CLDProjects，然后从匹配的记录中获取 CLD。

FROM {CLD} INNER JOIN (
    {CLDProjects} INNER JOIN {Project} ON  {Project}.[Id] = {CLDProjects}.[ProjectId]
  ) ON {CLD}.[Id] = {CLDProjects}.[CLDId]

Answer 2

您可能在 ProjectParticipant 子查询上缺少到 CLDProjects 的内部联接。添加

INNER JOIN {CLDProjects} ON {ProjectParticipant}.[ProjectId] =  {CLDProjects}.[ProjectId])

关于第二个 EXISTS 连接条件，否则第二个结果将匹配用户所在的每个项目的存在，而忽略 CLDProjects 上的其他条件。尝试以下操作：

SELECT {CLD}.[Id], {CLD}.[Name], {CLD}.[Comments]
      , {CLD}.[LastUpdateOn],min({Project}.[Number])
      ,count({Project}.[Number])
 FROM {CLD}
     INNER JOIN {Project} ON  {Project}.[Id] = {CLDProjects}.[ProjectId] 
     INNER JOIN {CLDProjects} ON {CLD}.[Id] = {CLDProjects}.[CLDId]
 WHERE 
   (
     @IsJAXPM =1 
     or EXISTS (SELECT 1 
             FROM {CLDParticipant} 
             WHERE {CLDParticipant}.[CLDId] = {CLD}.[Id] 
               AND {CLDParticipant}.[UserId] = @UserId) 
     or EXISTS (SELECT 1 
                FROM {ProjectParticipantWidget} 
                    INNER JOIN {ProjectParticipant} ON {ProjectParticipantWidget}.[ProjectParticipantId] =  {ProjectParticipant}.[Id]

                    INNER JOIN {CLDProjects} ON {ProjectParticipant}.[ProjectId] =  {CLDProjects}.[ProjectId]

                WHERE {ProjectParticipant}.[ProjectId] = {Project}.[Id] 
                  AND {ProjectParticipant}.[UserId] = @UserId)
   )
 GROUP BY {CLD}.[Id], {CLD}.[Name], {CLD}.[Comments], {CLD}.[LastUpdateOn]

另外.. 确保您没有将@IsJAXPM 作为 1 传递...否则它肯定会 return 所有记录。让我们知道这是否有效。否则，请扩展图表以同时显示 ProjectParticipant 和 ProjectParticipantWidget 表。

Answer 3

我认为你只需要重新排序你的连接，我试图重现你的情况（连接顺序不正确），但是在测试查询时它给了我错误，

但如果您重新排序连接，它就可以工作。请注意，我使用的是 OutSystems 10

问题理解内部连接或左连接

Issue understanding the Inner Join Or Left join

mysql

outsystems