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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8a8c857a6b005907e3d0f9597395ca123668fcf083180bc70989b2bff8deead3' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00032

JSON explain

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