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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '4103b54a5a26b9948f83fd2a743c7a3ec6efb8256615ffb4511bb8f00a7e335b' 
  AND token = 'rkdSrpWUUEsRTzURQlfSpH20//AVk3SPVgG1K0NDhqM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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