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SELECT 
  cscart_cp_object_location_rest.country_code 
FROM 
  cscart_cp_object_location_rest 
  LEFT JOIN cscart_countries ON cscart_countries.code = cscart_cp_object_location_rest.country_code 
WHERE 
  cscart_cp_object_location_rest.object_id = 6 
  AND cscart_cp_object_location_rest.object_type = 's' 
  AND cscart_cp_object_location_rest.country_code = 'US' 
  AND cscart_cp_object_location_rest.company_id = 0 
  AND cscart_countries.status = 'A'

Query time 0.00032

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}