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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51b27f5ae012c5912f2792f8a9e7fe3b3e90cc3b9e41a312a48640b615632a4f' 
  AND token = 'uxJKaCOjxDl+71Sx/GfeaB9R4OAEZfBDEbjXMcd7rus=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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