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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a51662076e4a8cd7fdbc9539fc9fc29abc1415f519ce4a71b95e43a9a1ad5415' 
  AND token = 'S0rYwD6z6GPocBq4X7ctj4OejxvtQiSdq8ZQ4inLm6o=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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