How to generate a random, unique, alphanumeric ID of length N in Postgres 9.6+?

Question

I\'ve seen a bunch of different solutions on StackOverflow that span many years and many Postgres versions, but with some of the newer features like gen_random_bytes I want

Answer 1

Thanks to Evan Carroll answer, I took a look on hashids.org. For Postgres you have to compile the extension or run some TSQL functions. But for my needs, I created something simpler based on hashids ideas (short, unguessable, unique, custom alphabet, avoid curse words).

Shuffle alphabet:

CREATE OR REPLACE FUNCTION consistent_shuffle(alphabet TEXT, salt TEXT) RETURNS TEXT AS $$
DECLARE
    SALT_LENGTH INT := length(salt);
    integer INT = 0;
    temp TEXT = '';
    j INT = 0;
    v INT := 0;
    p INT := 0;
    i INT := length(alphabet) - 1;
    output TEXT := alphabet;
BEGIN
    IF salt IS NULL OR length(LTRIM(RTRIM(salt))) = 0 THEN
        RETURN alphabet;
    END IF;
    WHILE i > 0 LOOP
        v := v % SALT_LENGTH;
        integer := ASCII(substr(salt, v + 1, 1));
        p := p + integer;
        j := (integer + v + p) % i;

        temp := substr(output, j + 1, 1);
        output := substr(output, 1, j) || substr(output, i + 1, 1) || substr(output, j + 2);
        output := substr(output, 1, i) || temp || substr(output, i + 2);

        i := i - 1;
        v := v + 1;
    END LOOP;
    RETURN output;
END;
$$ LANGUAGE plpgsql VOLATILE;

The main function:

CREATE OR REPLACE FUNCTION generate_uid(id INT, min_length INT, salt TEXT) RETURNS TEXT AS $$
DECLARE
    clean_alphabet TEXT := 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
    curse_chars TEXT := 'csfhuit';
    curse TEXT := curse_chars || UPPER(curse_chars);
    alphabet TEXT := regexp_replace(clean_alphabet, '[' || curse  || ']', '', 'gi');
    shuffle_alphabet TEXT := consistent_shuffle(alphabet, salt);
    char_length INT := length(alphabet);
    output TEXT := '';
BEGIN
    WHILE id != 0 LOOP
        output := output || substr(shuffle_alphabet, (id % char_length) + 1, 1);
        id := trunc(id / char_length);
    END LOOP;
    curse := consistent_shuffle(curse, output || salt);
    output := RPAD(output, min_length, curse);
    RETURN output;
END;
$$ LANGUAGE plpgsql VOLATILE;

How-to use examples:

-- 3: min-length
select generate_uid(123, 3, 'salt'); -- output: "0mH"

-- or as default value in a table
CREATE SEQUENCE IF NOT EXISTS my_id_serial START 1;
CREATE TABLE collections (
    id TEXT PRIMARY KEY DEFAULT generate_uid(CAST (nextval('my_id_serial') AS INTEGER), 3, 'salt')
);
insert into collections DEFAULT VALUES ;