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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51b7325942ae40ddbf548d57a5a86cc5856bb39b1ad2b2262af4b9ce7d0fc6ac' 
  AND token = 'd6TL6mcEYBS4ci3w2I0TTzD1OuvMloP6NXtDOZg8cWM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00015

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