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

Review,

1. 26 characters in [a-z]
2. 26 characters in [A-Z]
3. 10 characters in [0-9]
4. 62 characters in [a-zA-Z0-9] (base62)
5. The function substring(string [from int] [for int]) looks useful.

So it looks something like this. First we demonstrate that we can take the random-range and pull from it.

SELECT substring(
  'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
  1, -- 1 is 'a', 62 is '9'
  1,
);

Now we need a range between 1 and 63

SELECT trunc(random()*62+1)::int+1
FROM generate_series(1,1e2) AS gs(x)

This gets us there.. Now we just have to join the two..

SELECT substring(
  'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
  trunc(random()*62)::int+1
  1
)
FROM generate_series(1,1e2) AS gs(x);

Then we wrap it in an ARRAY constructor (because this is fast)

SELECT ARRAY(
  SELECT substring(
    'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
    trunc(random()*62)::int+1,
    1
  )
  FROM generate_series(1,1e2) AS gs(x)
);

And, we call array_to_string() to get a text.

SELECT array_to_string(
  ARRAY(
      SELECT substring(
        'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
        trunc(random()*62)::int+1,
        1
      )
      FROM generate_series(1,1e2) AS gs(x)
  )
  , ''
);

From here we can even turn it into a function..

CREATE FUNCTION random_string(randomLength int)
RETURNS text AS $$
SELECT array_to_string(
  ARRAY(
      SELECT substring(
        'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
        trunc(random()*62)::int+1,
        1
      )
      FROM generate_series(1,randomLength) AS gs(x)
  )
  , ''
)
$$ LANGUAGE SQL
RETURNS NULL ON NULL INPUT
VOLATILE LEAKPROOF;

and then

SELECT * FROM random_string(10);