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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b21717ef6d6100115c24e6b0a5fd496e797ebe7c8d8b4485df57c3874787d414' 
  AND token = 'Wl1YmBuWpfeFYMFqjFET6dy2cjoZWqkteuCisw9Az1A=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE								Impossible WHERE noticed after reading const tables