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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '256ddda1a60e027df713fde252fa40114dd0a6cd2546171308331666b9938a45' 
  AND token = '3XRPCSxhWq4e8gJ2dGJ5fXWlrC1BgumqOePk2tmWeYA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00049

JSON explain

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