SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b2b8f7bcd669884ce11c1be8f391f2a57e9d89a1ea09544290539db3a77cdce5' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}