Magento: First image as Shop Image

enable_shop_view_image.sql

# Find out the id to attribute_code "image" (here: 85)
# Find out the according entity_type_id (here: 4)

INSERT INTO catalog_product_entity_varchar (
  entity_type_id,
  attribute_id,
  entity_id,
  value
) (
  SELECT
    4 as entity_type_id,
    85 as attribute_id,
    entity_id,
    value
  FROM
    catalog_product_entity_media_gallery
  GROUP BY
    entity_id
)
ON DUPLICATE KEY UPDATE
    value=VALUES(value),
    entity_type_id=VALUES(entity_type_id)