SELECT 
  * 
FROM 
  cscart_profile_fields 
WHERE 
  profile_type = 'S' 
  AND is_default = 'Y'

Query time 0.00040

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_profile_fields",
      "access_type": "ALL",
      "rows": 49,
      "filtered": 100,
      "attached_condition": "cscart_profile_fields.profile_type = 'S' and cscart_profile_fields.is_default = 'Y'"
    }
  }
}