The following query generates random eight-character-long ASCII IDs (id_counts.id_counter pieces) using the specified alphabet (char_templates). The dash and underscore characters extend the alphanumeric alphabet to 64 characters allowing the selection of the six least significant bits from a random 64-bit number via bitwise AND (instead of mod). The ids block generates a 64-bit integer representation of the same ID. Saving character code before grouping in ascii_ids would not work because the query optimizer tends to rerun the query, executing the random function and generating the character and character code independently. The intermediate table aggregation operation prevents this optimization.

WITH
    id_counts(id_counter) AS (VALUES (3)),
    json_templates AS (SELECT '[' || replace(hex(zeroblob(id_counter*8-1)), '00', '0,') || '0]' AS json_template FROM id_counts),
    char_templates(char_template) AS (VALUES ('-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_')),
    ascii_ids AS (
        SELECT group_concat(substr(char_template, (random() & 63) + 1, 1), '') AS ascii_id, "key"/8 AS counter
        FROM char_templates, json_templates, json_each(json_templates.json_template) AS terms
        GROUP BY counter
    ),
    ids AS (
        SELECT counter, ascii_id,
               (unicode(substr(ascii_id, 1, 1)) << 8*7) +
               (unicode(substr(ascii_id, 2, 1)) << 8*6) +
               (unicode(substr(ascii_id, 3, 1)) << 8*5) +
               (unicode(substr(ascii_id, 4, 1)) << 8*4) +
               (unicode(substr(ascii_id, 5, 1)) << 8*3) +
               (unicode(substr(ascii_id, 6, 1)) << 8*2) +
               (unicode(substr(ascii_id, 7, 1)) << 8*1) +
               (unicode(substr(ascii_id, 8, 1)) << 8*0) AS bin_id
        FROM ascii_ids
    )
SELECT * FROM ids;

Sample output