Don't transform empty CSV table that was never created#736
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Closes simonw#702. A CSV that's only a header row leaves insert_all with no rows, so no table gets created. The follow-up transform(types=tracker.types) hit the 'Cannot transform a table that doesn't exist yet' assertion. Guard both insert paths on the table actually existing. Signed-off-by: Charlie Tonneslan <cst0520@gmail.com>
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Closes #702.
When a CSV file is header-only, `insert_all` is a no-op so the table never gets created, but the `--detect-types` path still calls `transform(types=tracker.types)` afterwards and `transform` asserts `table.exists()`. Result is the `AssertionError: Cannot transform a table that doesn't exist yet` traceback from the issue.
Gate the `transform` call on `table.exists()` so the empty case is a clean no-op. Applied the same guard to the analogous loop further down in `memory`-style multi-file insertion. Added a regression test that fails on main and passes here.
📚 Documentation preview 📚: https://sqlite-utils--736.org.readthedocs.build/en/736/