如何从另一个表中没有特定值的UID的表中选择*？

Question

I have two tables and what I'm trying to acheive is to grab a PhotoEmbed code from the Photos table so I can then use it to display a photo on the webpage - Each time the webpage is reloaded it will show a new picture. But I don't want to keep displaying the same picture?! I want to display a new picture each time...So I've set up the following tables but Have no idea how to run a query to actually grab the SELECT PhotoEmbed FROM Photos WHERE **CURRENT UserID** FROM Seen WHERE Seen **IS NOT EQUAL TO 1**

If the Seen is equal to 1 then run the query again and find a new PhotoEmbed code. Would you do this with a query or just select * from Photos and all from Seen and then USE PHP to determine what embed code to use?

Below Is a demo of two database tables. On the left there is the Photos Table and on the right (starting at userID) there is the Seen table.

| PhotoID | PhotoEmbed|    |UserID    | PhotoID |Seen |

| 1       |Filename.jpg|   |2         | 1       |1    |

Answer 1

Get all photos which are not in the seen table like this:

SELECT PhotoID,etc from Photos where PhotoID NOT IN (select PhotoID from Seen where UserId = 1)

Given if you insert only viewed images in Seen table ( seen column,which I guess is bool could be removed), if you insert a new image I don't suppose for each user you should populate the table with seen set to 0.

If by any chance the user saw all images consider making a random fetch:

SELECT * FROM PhotosORDER BY RAND() LIMIT 1;