previously my boss gave me 8-digits, and when I used Digest::MD5, I got duplicated IDs
If you got duplicates in the output, you can be sure the list you used as input had duplicates also. Hashes like MD5 are designed to not produce collisions (different inputs producing same output).
Either that, or some programming error in your script using Digest::MD5.

In reply to Re^3: Question: Generate unique/random 12-digit keys for 25,000K records, howto?? by carol
in thread Question: Generate unique/random 12-digit keys for 25,000K records, howto?? by lihao

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