在 MySQL 查询中使用带有 Where 子句的案例

Question

我需要根据 where 子句加入 tables，基本上我有一个 table 的提要结构类似于下面，我只提到了必要的列，因为有不需要在此处显示的大量列

feed_id | type_id | user_id | timestamp

我正在使用下面的查询来获取结果。

SELECT feed.*
FROM `phpfox_feed` feed
JOIN `phpfox_user` u ON u.user_id = feed.user_id
Left Join `phpfox_friend` f  ON feed.user_id = f.user_id AND f.friend_user_id = 441
Left Join `phpfox_app` apps  ON feed.app_id = apps.app_id
Where feed.feed_reference = 0 
      AND feed.type_id in ("forum","blog","event","news","video","pages_created")

在 type_id 中显示结果，即：新闻、事件、组、博客

所以我希望如果行有 'feed_type' = news 然后它加入特定的 tables，类似地如果行有 'feed_type' = 组它加入其他 table s，比如我下面提到新闻和群的情况

案例新闻：

Join phpfox_news ON phpfox_news.feed_id = feed.feed_id
Join phpfox_news_cateogries 
            ON phpfox_news.cateogry_id = phpfox_news_cateogries.cateogry_id
Where phpfox_news_cateogries.category_name in ("sports","politics","party")

案例组：

Join phpfox_group ON phpfox_group.feed_id = feed.feed_id
Where phpfox_group.category_name in ("sports","politics","party")

我试过的

我使用我在 Where I Stuck 中提到的示例尝试了以下操作，但它给了我一个错误

SELECT feed.*
FROM `phpfox_feed` feed
JOIN `phpfox_user` u ON u.user_id = feed.user_id
Left Join `phpfox_friend` f  ON feed.user_id = f.user_id AND f.friend_user_id = 441
Left Join `phpfox_app` apps  ON feed.app_id = apps.app_id
Where feed.feed_reference = 0 
     AND feed.type_id in ("forum","blog","event","news","video","pages_created") 
  AND               
Case                
   When feed.type_id = "news" 
    Then Join phpfox_news ON phpfox_news.feed_id = feed.feed_id
         Join phpfox_news_cateogries 
             ON phpfox_news.cateogry_id = phpfox_news_cateogries.cateogry_id
          Where phpfox_news_cateogries.category_name in ("sports","politics","party")

   When feed.type_id  = "group" 
    Then Join phpfox_group ON phpfox_group.feed_id = feed.feed_id
        Where phpfox_group.category_name in ("sports","politics","party")
            
End

我卡在哪里

我发现的是 SQL 查询中的一个案例，但我发现它只支持 select 或像下面的例子所示的连接，我按照上面的尝试

    Select LNext.player As NextPlayer
    From lineups As L
    Left Join lineups As LNext
    On LNext.BattingOrder Between 11 And 20
        And LNext.BattingOrder  = Case
                                    When L.BattingOrder  = 19 Then 11
                                    Else L.BattingOrder  + 1
                                    End
    Where L.battingOrder Between 11 And 20

查询

这种查询可以与 MySQL 中的 'Cases' 一起使用吗？
如何使用带有 where 子句的 Case 来实现我的结果

Answer 1

尝试加入表，同时添加条件 feed.type_id 成为合适的类型。

而不是做：

When feed.type_id = "news" Then Join phpfox_news ON phpfox_news.feed_id = feed.feed_id

尝试：

Join phpfox_news ON phpfox_news.feed_id = feed.feed_id AND feed.type_id = "news"

因此您尝试运行的查询应更改为：

SELECT feed.*
FROM `phpfox_feed` feed
JOIN `phpfox_user` u ON u.user_id = feed.user_id
Left Join `phpfox_friend` f  ON feed.user_id = f.user_id AND f.friend_user_id = 441
Left Join `phpfox_app` apps  ON feed.app_id = apps.app_id
Left Join phpfox_news ON phpfox_news.feed_id = feed.feed_id AND feed.type_id = "news"
Left Join phpfox_news_cateogries ON phpfox_news.cateogry_id = phpfox_news_cateogries.cateogry_id
          AND phpfox_news_cateogries.category_name in ("sports","politics","party")
Left Join phpfox_group ON phpfox_group.feed_id = feed.feed_id AND feed.type_id  = "group" AND  phpfox_group.category_name in ("sports","politics","party")
Where feed.feed_reference = 0 
     AND feed.type_id in ("forum","blog","event","news","video","pages_created")

Answer 2

根据@hofan41 提到的指南，我使用以下查询从两个不同的连接中获取结果

SELECT feed.*
FROM `phpfox_feed` feed
JOIN `phpfox_user` u ON u.user_id = feed.user_id
Left Join `phpfox_friend` f  ON feed.user_id = f.user_id AND f.friend_user_id = 441
Left Join `phpfox_app` apps  ON feed.app_id = apps.app_id

Left Join phpfox_news_items ON phpfox_news_items.item_id = feed.item_id AND feed.type_id = "news"

Left Join phpfox_news_feeds ON phpfox_news_feeds.feed_id = phpfox_news_items.feed_id

Left Join phpfox_news_categories ON phpfox_news_categories.category_id = phpfox_news_feeds.category_id

Left Join phpfox_pages ON phpfox_pages.page_id = feed.item_id AND feed.type_id = "pages_created"          
LEFT JOIN phpfox_pages_type ON phpfox_pages_type.type_id = phpfox_pages.type_id

Where feed.feed_reference = 0 
AND feed.type_id in ("forum","blog","event","news","video","pages_created") AND (phpfox_news_categories.category_name in ("Movies","music") OR phpfox_pages_type.name in ("Movies","music"))
ORDER BY `feed`.`item_id`  ASC

在 MySQL 查询中使用带有 Where 子句的案例

Use of Cases with Where clause in MySQL query

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