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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a21cddb69336c48055fe09bccee5a4080a1f82f705b124375257f022f8626e2c' 
  AND token = 'RFXAelTbEClomGjRgplgbh3fz9zVuBrXdac80IKFYDE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00041

JSON explain

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