fix: reject zero-column table creation

src/metadata_writer_sqlite.rs

@@ -204,6 +204,11 @@ impl MetadataWriter for SqliteMetadataWriter {
         columns: &[ColumnDef],
         snapshot_id: i64,
     ) -> Result<Vec<i64>> {
+        if columns.is_empty() {
+            return Err(crate::DuckLakeError::InvalidConfig(
+                "Table must have at least one column".to_string(),
+            ));
+        }
         block_on(async {
             // Use a transaction to ensure atomicity: if column insertion fails,
             // we don't leave existing columns marked as ended
@@ -328,6 +333,11 @@ impl MetadataWriter for SqliteMetadataWriter {
         columns: &[ColumnDef],
         mode: WriteMode,
     ) -> Result<WriteSetupResult> {
+        if columns.is_empty() {
+            return Err(crate::DuckLakeError::InvalidConfig(
+                "Table must have at least one column".to_string(),
+            ));
+        }
         block_on(async {
             let mut tx = self.pool.begin().await?;
 

tests/write_tests.rs

@@ -909,3 +909,26 @@ async fn test_append_reorder_columns() {
         .value(0);
     assert_eq!(count, 4);
 }
+
+#[tokio::test(flavor = "multi_thread")]
+async fn test_zero_column_table_rejected() {
+    let (writer, _temp_dir) = create_test_env().await;
+    let object_store = create_object_store();
+
+    // An empty Arrow schema (zero columns)
+    let schema = Arc::new(Schema::empty());
+
+    let batch = RecordBatch::new_empty(schema.clone());
+
+    let table_writer = DuckLakeTableWriter::new(Arc::new(writer), object_store).unwrap();
+    let result = table_writer
+        .write_table("main", "empty_cols", &[batch])
+        .await;
+    assert!(result.is_err(), "Zero-column table should be rejected");
+    let err = result.unwrap_err().to_string();
+    assert!(
+        err.contains("at least one column"),
+        "Error should mention needing at least one column: {}",
+        err
+    );
+}