Question

我有四张桌子 1. tbl_threads 2. tbl_comments 3. tbl_votes 4. tbl_users

假设当前登录的user_id = 3 thread_id = 10

现在我必须检索以下数据

All the fields from tbl_comments where tbl_comments.thread_id =10
All the fields from tbl_users based on the common key tbl_users.user_id = tbl_comments.user_id
All the fields from tbl_votes Where user_id =3 And tbl_votes.comment_id =tbl_comments.comment_id

如何使用一个查询执行所有此功能？

我尝试了以下查询，但它给了我错误的结果

SELECT tbl_comments.*
     , tbl_users.*
     , tbl_votes.* 
FROM tbl_comments 
INNER JOIN tbl_users 
on tbl_comments.user_id = tbl_users.user_id 
WHERE thread_id= 10
INNER JOIN tbl_votes 
on tbl_votes.comment_id = tbl_comments.comment_id 
WHERE tbl_votes.user_id= 3

Answer 1

假设列thread_id位于tbl_comments表中，请将第一个where更改为and：

SELECT tbl_comments.*
     , tbl_users.*
     , tbl_votes.* 
FROM tbl_comments 
INNER JOIN tbl_users 
on tbl_comments.user_id = tbl_users.user_id 
and  tbl_comments.thread_id= 10
INNER JOIN tbl_votes 
on tbl_votes.comment_id = tbl_comments.comment_id 
WHERE tbl_votes.user_id= 3

虽然您的问题提到了一个名为tbl_threads的表，但您的示例中没有显示任何对它的引用。

Answer 2

SELECT O.OrderNumber, CONVERT(date,O.OrderDate) AS Date, 
       P.ProductName, I.Quantity, I.UnitPrice 
  FROM [Order] O 
  JOIN OrderItem I ON O.Id = I.OrderId 
  JOIN Product P ON P.Id = I.ProductId
ORDER BY O.OrderNumber

INNER JOIN和WHERE子句中的三个表

2 个答案: