fix: rel_sql(rel, "{{sql}}") works even on a read-only database

[Tmonster]

If a user attempts to query a read only database with rel_sql they will encounter an error. This is because rel_sql creates a view with name _.

The fix is to make this a temporary view. If the user still tries to create a table with create table as (select * from _) an error should still be thrown

Fixes https://github.com/duckdblabs/duckdb-internal/issues/1721

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.73%. Comparing base (0118ae4) to head (ed32009).

❗ Current head ed32009 differs from pull request most recent head 3bb53c3. Consider uploading reports for the commit 3bb53c3 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #138      +/-   ##
==========================================
+ Coverage   79.70%   79.73%   +0.02%     
==========================================
  Files         108      108              
  Lines        3711     3711              
==========================================
+ Hits         2958     2959       +1     
+ Misses        753      752       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[krlmlr]

Thanks!

[krlmlr]

@Tmonster: I realized too late that this patches the duckdb sources. Has this been upstreamed by now? Do you want to?

I can work around with a patch file for now.

[Tmonster]

has not been upstreamed yet, and might not be until after v1.0 comes out. I think a patch file in duckdb-r is the way to go for now. I will still create an upstream PR though so you can eventually remove that patch.