SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '621867fd4086050f8484151c2001b2f222d4664f2fd31e278bd84089c4ffab0f' 
  AND token = 'VEiu5BIvHEV0UgtJ8ejv+LLLEatNq+BlCMMYGNGqTCE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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