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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'a8d92363bd421250f11954d028ae2fb6eb4ae5e018bc6f2b912998a88b27e5ff' 
  AND token = 'QUTHoutvT/bZJa4Q3VJAPxE8Iq9Xl4Xsv4i9/EJTMTg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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