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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '503b736b36d7c029c870f5db207fbcd30ce71e2b3209b2d428a9bcbc664a3271' 
  AND token = '/JYURLMVa8E1KsguSkgMn+ovSzeqms0avsO6e/MroPU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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