SELECT 
  * 
FROM 
  cscart_csc_sync_rates 
WHERE 
  1 
  AND cscart_csc_sync_rates.company_id = 0

Query time 0.00010

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_csc_sync_rates",
      "access_type": "ALL",
      "rows": 1,
      "filtered": 100,
      "attached_condition": "cscart_csc_sync_rates.company_id = 0"
    }
  }
}