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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '31c0bd25853fb453c01b76bd5ede08c2f78a3dbb1e3e378329dd93e02fff9969' 
  AND token = 'PYWRQ+a3gdiBV8Eptr5pAS6Jw/2fTuBkTNDYk9B4jaI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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