內部連接兩行後不工作？

Question

這是我的查詢，它不顯示第三行，即使表內容匹配。

SELECT shopcategory_idcategory_name 
FROM shopcategory 
INNER JOIN category ON shopcategory_id=category_id; 

結果：

================================================================ 
| shopcategory_id | shopcategory_shopid | category_name | 
================================================================ 
|  1  |   1   |  Gadgets  | 
|  2  |   2   |  Analog Device | 
================================================================ 

這裏是我的查詢，顯示有3行

SELECT * FROM shopcategory; 

結果：

=================================================================== 
| shopcategory_id | shopcategory_shopid | shopcategory_categoryid | 
=================================================================== 
|  1   |   1   |   1   | 
|  2   |   2   |   2   | 
|  3   |   3   |   3   | 
=================================================================== 

編輯：查詢我的類別表

SELECT * category; 

結果：

============================================== 
| category_id |  category_name  | 
============================================== 
|  1   |  Gadgets   | 
|  2   |  Analog Device  | 
|  3   |   Beauty   | 
|  4   |  Keyboard  | 
|  5   |  Instruments  | 
|  6   |   Monitor  | 
|  7   |   Chairs   | 
============================================== 

Answer 1

你應該在這裏使用LEFT JOIN代替，並添加aliases爲要加入的表上，這樣：

SELECT 
    tableName1.shopcategory_id, 
    tableName1.category_name, 
    tableName2.category_id 
FROM 
    tableName1 as tb1 
LEFT JOIN 
    tableName2 AS tb2 
ON 
    tb1.shopcategory_id = tb2.category_id 
GROUP BY 
    tb1.shopcategory_id;