lexographical.ts

const charset = ['a', 'b', 'c'];

function parse(key: string): number[] {
	return key.split('').map(c => charset.indexOf(c));
}

function format(key: number[]): string {
	return key.map(i => charset[i]).join('');
}

function increment(key: number[]): void {
	let last = key[key.length - 1];
	if (last === charset.length - 1) {
		key.push(0);
	} else {
		key.push(last + 1);
	}
}

function decrement(key: number[]): void {
	// ?
}

function generate(lo: string, hi: string): string {
	let inc = format(increment(parse(low))),
		dec = format(decrement(parse(hi)));
	return inc < hi ? inc : dec;
}

rank.sql

-- create table
CREATE TABLE test (
	id   bigserial,
	rank bigint
);

-- rebalance ranks
UPDATE test
SET rank = (v_test.row_num * 1000)
FROM (
	SELECT id, ROW_NUMBER() OVER (ORDER BY rank) as row_num
	FROM test
) AS v_test
WHERE test.id = v_test.id;