Retrieving a list of rows with only a single item from other table in Oracle - oracle

Question

I have two tables in Oracle database (10g express)
product
product_image
One product can have multiple images. Hence, there a one-to-many relationship from product to product_image and the product_image table has a foreign key that refers to the primary key of the product table.
I need to fetch a list of products with only a single image name in each row of the result set being retrieved regardless of the images being in the product_image table (even though there are no images for some of products).
The image name to be retrieved from the product_image table is generally the first image name in the product_image table after sorting each set of images for each product in ascending order. Something like the following.
prod_id prod_name prod_image
1 aaa aaa.jpg //The first image name in the product_image table after sorting images for prod_id in ascending order.
2 bbb bbb.jpg //Similar to the first case.
3 ccc - //No image(s) found in the product_image table
4 ddd - //Similar to the previous case.
The general join statement for these two tables would be something similar to the following.
SELECT p.prod_id, p.prod_name, pi.prod_image
FROM product p
INNER JOIN product_image pi
ON p.prod_id=pi.prod_id;
Is this possible using a single SQL statement?

Answer 1

If I understood your question correctly I think the following query will work. I have not tested it.
SELECT p.prod_id, p.prod_name, MIN(DBMS_LOB.substr(pi.prod_image, 1))
FROM product p LEFT JOIN product_image pi
ON p.prod_id=pi.prod_id
GROUP BY p.prod_id, p.prod_name
ORDER BY p.prod_name;

Answer 2

Try this, you can generate row number for each image per prod_id and use that. To return null or blank from missing product image you should use left outer join
WITH CTE AS
(
SELECT prod_id, DBMS_LOB.substr(prod_image,1,4000) prod_image,
row_number() over (partition by prod_id order by prod_image) rn
FROM product_image
)
SELECT p.prod_id, p.prod_name, nvl(pi.prod_image,'-') prod_image
FROM product p
LEFT OUTER JOIN CTE pi
ON p.prod_id=pi.prod_id and pi.rn = 1;

Answer 3

The following SQL worked as mentioned in the question.
SELECT
p.prod_id,
p.prod_name,
t.prod_image
FROM
product p
LEFT OUTER JOIN(
SELECT
pi.prod_image_id,
pi.prod_id,
pi.prod_image
FROM
product_image pi
INNER JOIN (
SELECT
MIN(pi.prod_image_id) AS prod_image_id
FROM
product_image pi
GROUP BY
pi.prod_id
) prod_image
ON pi.prod_image_id=prod_image.prod_image_id
)t ON p.prod_id=t.prod_id ORDER BY p.prod_id DESC;
Reference:
SQL Select only rows with Max Value on a Column