MySQL，根据列值从其他行中选择

Question

I have the following table

---------------------------
|ID  |Image      | link    |
|01  |           | 02      |  
|02  |steve.jpg  |         |         
|03  |eric.jpg   |         |         
----------------------------

The link field stores IDs, so I can set a relationship between two rows.

The ID 01 has its link field set to 02. So I want ID 01 to use the image whose ID is set in that field, so it'll be steve.jpg.

How can I get all rows, so that the ones with the link field set end up with that Image?

Answer 1

You can use self join in order to show the image name for link id

select t.*,t1.Image as link_image
from t 
left join t t1 on(t.link = t1.ID)

Demo

Answer 2

SELECT a.id, b.image, a.link
FROM YourTable AS a
JOIN YourTable AS b ON a.link = b.id
UNION
SELECT id, image, link
FROM YourTable
WHERE link IS NULL

Answer 3

Something like this:

(SELECT ID, Image from mytable WHERE link = '' )
UNION ALL
(SELECT m1.ID as ID, m2.Image as Image 
   FROM mytable AS m1 INNER JOIN mytable AS m2 ON ( m1.link=m2.ID )
)