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SELECT 
  1 
FROM 
  cscart_aprillock_keys 
WHERE 
  key_id = '3681b4d45a173641781563ac0a3dec2e0a53af1bb882ca422274e28954aabbbc' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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