如何使用随机列MYSQL选择Distinct？

Question

I've table books that contains image, language, faith. I'am getting distinct values for faith with

SELECT DISTINCT faith, language from books;

That fetches faith series ( 15 results ) but I want to fetch image along too but randomly. So the result can be able to show faith with random image. How I can do that, please suggest.

Answer 1

The query

select distinct faith, language from books;

selects distinct Faith-Language combinations from your table. So where your table contains two entries for the same Faith and Language

Faith  Language  Image
1      EN        img1
1      EN        img2
1      FR        img3
1      FR        img4

your result would contain each combination just once:

Faith  Language
1      EN
1      FR

It is not clear from your question yet, what you mean with a random image. Here is how you get one of the matching images for a Faith-Language combination arbitrarily picked:

select faith, language, image
from books
group by faith, language;

The result could look like this:

Faith  Language  Image
1      EN        img2
1      FR        img3

The reason is that we aggregate the rows. In the GROUP BY clause we say we want one result row per Faith and Language, but we also select Image and don't specify which one we'd like to see per group (which we could do with an aggregate function like MIN or MAX), so we just get one of the images matching the Faith-Language combination arbitrarily picked by the DBMS.

Is this already what you want?

Answer 2

Thank to everybody, i got the solution from

Select random row per distinct field value?

SELECT r.faith, 
(SELECT r1.image FROM books AS r1 WHERE r.faith=r1.faith ORDER BY rand() LIMIT 1) AS image FROM books AS r GROUP BY r.faith;  

it's fetching distinct field1 faith with random field2 image against each faith everytime query executed.