A way of creating indexes on newly created tables

I'm writing code for https://github.com/simonw/git-history/issues/33 that creates a table inside a loop:

item_pk = db[item_table].lookup(
    {"_item_id": item_id},
    item_to_insert,
    column_order=("_id", "_item_id"),
    pk="_id",
)

I need to look things up by _item_id on this table, which means I need an index on that column (the table can get very big).

But there's no mechanism in SQLite utils to detect if the table was created for the first time and add an index to it. And I don't want to run CREATE INDEX IF NOT EXISTS every time through the loop.

This should work like the foreign_keys= mechanism.

Start by tracing the db[item_table].lookup() entry point and the existing foreign_keys= mechanism. Define how indexes should be supplied when a table is first created, ensure repeated loop iterations do not recreate them, and verify that lookups by _item_id use the new index.