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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6b639701d1d88a91d111989864f952212b15706e047ff305d3a35a9da388a04f' 
  AND token = 'gzZk2356i4pn4MfftbGPp0RvBeMYo4tuoIfoEcMhMq0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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