Fix: CSV insert with --detect-types crashes on header-only CSV

When using --detect-types with a CSV file containing only a header row
(and no data rows), the insert would fail with 'Cannot transform a table
that doesn't exist yet' because the table is only created when rows are
inserted. This fix adds an existence check before attempting to transform.

Fixes #702

Author: Test User

sqlite_utils/cli.py

@@ -1176,7 +1176,7 @@ def insert_upsert_implementation(
                 )
             else:
                 raise
-        if tracker is not None:
+        if tracker is not None and db.table(table).exists():
             db.table(table).transform(types=tracker.types)
 
         # Clean up open file-like objects
@@ -2033,7 +2033,7 @@ def memory(
                 rows = (_flatten(row) for row in rows)
 
             db.table(file_table).insert_all(rows, alter=True)
-            if tracker is not None:
+            if tracker is not None and db.table(file_table).exists():
                 db.table(file_table).transform(types=tracker.types)
             # Add convenient t / t1 / t2 views
             view_names = ["t{}".format(i + 1)]

tests/test_cli_insert.py

@@ -597,3 +597,19 @@ def try_until(expected):
     proc.stdin.close()
     proc.wait()
     assert proc.returncode == 0
+
+
+def test_insert_csv_header_only(tmpdir):
+    # https://github.com/simonw/sqlite-utils/issues/702
+    # Inserting a CSV with only a header row (no data) and --detect-types
+    # should not crash
+    db_path = str(tmpdir / "test.db")
+    result = CliRunner().invoke(
+        cli.cli,
+        ["insert", db_path, "data", "-", "--csv", "--detect-types"],
+        input="foo,bar,baz",
+    )
+    assert result.exit_code == 0, result.output
+    # Table should not exist since no rows were inserted
+    db = Database(db_path)
+    assert "data" not in db.table_names()