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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21a6e11b6903ecbe161ac1de2185c02d922889bf743e3cfd561870827af57619' 
  AND token = '4BusrEmndicq5qEVXMhUt+ehH68cpeVDh9XwWWVlKrY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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