MidLifeXis:

It doesn't have to be nested. SQLite is fine with insert (cols) select ...:

14:28 METABASE.DFLT:
create table foo (a int, b text);
0 affected, 1 sec.

create table bar (a int, b text);
0 affected, 0 sec.

insert into bar (a, b) values (1, 'bing')
1 affected, 0 sec.

insert into bar (a, b) values (2, 'bop')
1 affected, 0 sec.

insert into foo (a, b) select a, b from bar
2 affected, 0 sec.

select * from foo
a b
1 bing
2 bop
2 rows
elapsed time: 0
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...roboticus

When your only tool is a hammer, all problems look like your thumb.