sql - 如何在左连接中选择单个记录

Question

我需要使用其关键 ModelID 从模型表中选择特定模型。我还需要添加 Model_Content 表中的内容简介。然而，Models_Content 表对于每个模型都有几个内容简介。我只需选择第一个简介。

我的表格如下所示:

 Models // table
 ModelID // pk
 Model // varchar

 Models_Content // table
 ContentID // pk
 ModelID // fk
 Content // varchar

 SELECT M.ModelID, M.Model, C.Content
 FROM   Models M LEFT JOIN Models_Content C ON M.ModelID =  C.ModelID
 WHERE      M.ModelID = 5

如何调整查询以仅选择特定模型的第一个内容简介？

Answer 1

 SELECT
   M.ModelID, M.Model, C.Content
 FROM
   Models M
 LEFT JOIN
   Models_Content C
     ON C.ContentID = (SELECT MIN(ContentID) FROM Models_Content WHERE ModelID = M.ModelID)
 WHERE
   M.ModelID = 5

或者

;WITH sorted_content AS
(
  SELECT
    ROW_NUMBER() OVER (PARTITION BY ModelID ORDER BY ContentID) AS itemID,
    *
  FROM
    Models_Content
)
 SELECT
   M.ModelID, M.Model, C.Content
 FROM
   Models M
 LEFT JOIN
   sorted_content C
     ON  C.ModelID = M.ModelID
     AND C.itemID  = 1
 WHERE
   M.ModelID = 5