How much length can be of a Telegram user_id?

Question

I am making a database in which my algorithm only accepts queries from users with telegram id length of 9.

user_id: 123456789;
length = user_id.length;
display(length);

OUTPUT: 9

Are there telegram user ids of length lesser than 9?
Can anybody suggest something, so that i can update my algorithm to length of that ids too.

Answer 1

You can refer to Contact section of API document.

it has at most 52 significant bits, so a 64-bit integer or double-precision float type are safe for storing this identifier.

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2018 (Outdated):

There have no known limit of user ID, but I know there have some user have less than 9 digits ID.

For instance, @MarkusRa have 6-digits ID.

The maximum length I have seen is 9 digits, and starts with 6, it seems to increase by time, maybe it will have 10 digits soon