SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '7b5c37e42ebe2959682aaccd3097b100af66a2cf704bca96e42ce659824f68b1' 
  AND token = 'W23z3sU1BVwJKdSOp7tKUcjQ7NzJ0AFVQ3JWFXiG8gk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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