SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50cc19e88806b619b6dbda196ea979e5450d819117df5730e162373ee8341364' 
  AND token = '9iNdTRWduzdkMMNXGuHpKQWdvpsLmMsmhk4misQmvK4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}