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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'd51e055a2d65fc7c185f09912dcf5269d319a8844bfba5774b41dda490399543' 
  AND token = 'MDTj8ry4zsyJDwgN95NE01zdsZrAU3NWRZywk2BrJZE=' 
  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