Add short alphanumeric public_id from integer

[andyatkinson]

Wanted the following properties:

• source column is an integer (4 bytes)
• Fixed size output for public_id, 5 characters of length, regardless of length of integer
• public_id is a text (not char(5) per PostgreSQL "don't do this"), 1 byte per char, so 5 bytes for the chars
• obfuscated, non-incrementing, not easily "guessable". Although, not intended to be a "secure" solution.
• The public_id can be reversed into the original integer value
• Only PL/PgSQL functions, Postgres data types, unique, not null, and check constraints, no extensions needed
• Implementation is not math-heavy. It uses some bits conversion. Converts to bits. Inverts bits (XOR).

This seems to fit the bill and has these functions:

• obfuscate_id(id INTEGER)
• to_base62_fixed(val BIGINT, width INT DEFAULT 5)
• deobfuscate_id(public_id TEXT)
• from_base62_fixed(str TEXT)

For 5 char values, we could do up to ~1 billion values

For 6 char values, we could do up to ~56 billion values

[andyatkinson]

Updates needed:

• Don't use char(5) use text
• Could add a CHECK constraint that validates the length of the input (although it's from an internal function, so maybe overkill)

Source: https://wiki.postgresql.org/wiki/Don't_Do_This