fix(duckdb): disallow creating null-typed columns with duckdb

ibis/backends/duckdb/__init__.py

@@ -169,6 +169,16 @@ def create_table(
         else:
             query = None
 
+        if schema is None:
+            schema = table.schema()
+
+        if schema.nulls:
+            raise exc.UnsupportedBackendType(
+                "DuckDB does not support creating tables with NULL typed columns. "
+                "Ensure that every column has non-NULL type. "
+                f"NULL columns: {schema.nulls}"
+            )
+
         column_defs = [
             sge.ColumnDef(
                 this=sg.to_identifier(colname, quoted=self.compiler.quoted),
@@ -179,7 +189,7 @@ def create_table(
                     else [sge.ColumnConstraint(kind=sge.NotNullColumnConstraint())]
                 ),
             )
-            for colname, typ in (schema or table.schema()).items()
+            for colname, typ in schema.items()
         ]
 
         if overwrite:

ibis/backends/duckdb/tests/test_client.py

@@ -11,6 +11,7 @@
 from pytest import param
 
 import ibis
+import ibis.common.exceptions as com
 import ibis.expr.datatypes as dt
 from ibis.conftest import LINUX, SANDBOXED, not_windows
 from ibis.util import gen_name
@@ -403,3 +404,22 @@ def test_read_csv_with_types(tmp_path, input, all_varchar):
     path.write_bytes(data)
     t = con.read_csv(path, all_varchar=all_varchar, **input)
     assert t.schema()["geom"].is_geospatial()
+
+
+def test_create_table_with_nulls(con):
+    t = ibis.memtable({"a": [None]})
+    schema = t.schema()
+
+    assert schema == ibis.schema({"a": "null"})
+    assert schema.nulls == ("a",)
+
+    name = gen_name("duckdb_all_nulls")
+
+    with pytest.raises(com.UnsupportedBackendType, match="NULL typed columns"):
+        con.create_table(name, obj=t)
+
+    with pytest.raises(com.UnsupportedBackendType, match="NULL typed columns"):
+        con.create_table(name, obj=t, schema=schema)
+
+    with pytest.raises(com.UnsupportedBackendType, match="NULL typed columns"):
+        con.create_table(name, schema=schema)