使用內部連接選擇最后一行

Question

我有兩個關系表 [category] ​​和 [briefs]。 我想從簡報中選擇最后一行 WHERE Briefs.category_id = category.category_id;

[Category]
category_id
category_name

[briefs]
brief_id
category_id
brief_file_num
brief_date



 "SELECT brief_file_num,category_id FROM briefs,category 
WHERE briefs.category_id = category.category_id ORDER BY briefs.brief_file_num 
DESC LIMIT 1";

我收到以下錯誤： "Column 'category_id' in field list is ambiguous"

Answer 1

即使兩個類別具有相同的值。 您還需要指定您引用的表，因為兩者都有一個具有該名稱的列

也使用顯式JOIN sintaxis，Aaron Bertrand 寫了一篇很好的文章踢壞習慣：使用舊式 JOIN關於它。

 SELECT briefs.brief_file_num,
        briefs.category_id    
 FROM briefs
 INNER JOIN category 
    ON briefs.category_id = category.category_id 
 ORDER BY briefs.brief_file_num 
 DESC LIMIT 1"

Answer 2

兩個表都有一個category_id ，這是不明確的。 使用category.category_id代替！

SELECT brief_file_num,category.category_id FROM briefs,category 
WHERE briefs.category_id = category.category_id ORDER BY briefs.brief_file_num 
DESC LIMIT 1

Answer 3

您應該明確添加表名以避免歧義

   "SELECT briefs.brief_file_num, briefs.category_id 
     FROM briefs,category 
     WHERE briefs.category_id = category.category_id ORDER BY briefs.brief_file_num 
    DESC LIMIT 1";