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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b51b9b8beed9c46e1e8e25fd346929bc44c7b24fc294b5709ffbe8c2f4cce166' 
  AND token = 'a7cjiEVW8fAAIk6rWx74Tfn/4edI38mrCtYj/9ye+MY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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