SELECT 
  processor_id 
FROM 
  cscart_payment_processors 
WHERE 
  processor_script = 'vnpay_credit.php'

Query time 0.00087

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_payment_processors",
          "access_type": "ALL",
          "rows": 69,
          "filtered": 100,
          "attached_condition": "cscart_payment_processors.processor_script = 'vnpay_credit.php'"
        }
      }
    ]
  }
}