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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '5166c9176ea2fdf88bf4f36a35e2bd43dd7cf08f39def2a98e46c4f912a51dc9' 
  AND token = 'smdCOKVWkU6rymmbf9GjoJBIBBRDnKle7nKiIZYVAsE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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