Bdtyktl

I have nearly 40k products and all images have been set to small only. If I go into the backend and then set each image one by one to the base, it will take me forever. Is there any way to do it via the database?

If you want to do by MySQL way follow below way

First, run below query to know the query is actually working and you will get a list of images

select  ev.value, mg.value from catalog_product_entity_media_gallery AS mg,

catalog_product_entity_media_gallery_value AS mgv,

catalog_product_entity_varchar AS ev

WHERE  mg.value_id = mgv.value_id

AND mgv.entity_id = ev.entity_id

AND ev.attribute_id IN (87, 88, 89)

AND mgv.position = 1; 

After that run below query to update small image path with a thumbnail image

UPDATE catalog_product_entity_media_gallery AS mg,

catalog_product_entity_media_gallery_value AS mgv,

catalog_product_entity_varchar AS ev

SET ev.value = mg.value

WHERE  mg.value_id = mgv.value_id

AND mgv.entity_id = ev.entity_id

AND ev.attribute_id IN (87, 88, 89)

AND mgv.position = 1; 

You should run first in test ENV, after making sure you can run on other ENV.

Hope It will solve your issue

You can use the CSV.
Please add two more column 'base_image' and 'thumbnail_image' in the csv file and re import all the products.Then after reindex the process.