SELECT 
  profile_id 
FROM 
  cscart_user_profiles 
WHERE 
  user_id = 0 
ORDER BY 
  profile_id ASC 
LIMIT 
  1

Query time 0.00051

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "read_sorted_file": {
          "filesort": {
            "sort_key": "cscart_user_profiles.profile_id",
            "table": {
              "table_name": "cscart_user_profiles",
              "access_type": "ref",
              "possible_keys": ["uid_p"],
              "key": "uid_p",
              "key_length": "3",
              "used_key_parts": ["user_id"],
              "ref": ["const"],
              "rows": 1,
              "filtered": 100,
              "attached_condition": "cscart_user_profiles.user_id <=> 0"
            }
          }
        }
      }
    ]
  }
}