SELECT 
  object_id 
FROM 
  cscart_images_links 
WHERE 
  object_type = 'abt__yt_mwi__icon'

Query time 0.00156

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_images_links",
      "access_type": "index",
      "key": "object_id",
      "key_length": "81",
      "used_key_parts": ["object_id", "object_type", "type"],
      "rows": 7248,
      "filtered": 100,
      "attached_condition": "cscart_images_links.object_type = 'abt__yt_mwi__icon'",
      "using_index": true
    }
  }
}