fix(driver): better handle null datatype (#100)

driver/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "databend-driver"
-version = "0.2.20"
+version = "0.2.21"
 edition = "2021"
 license = "Apache-2.0"
 description = "Databend Driver for Rust"

driver/src/schema.rs

@@ -139,7 +139,7 @@ impl TryFrom<&TypeDesc<'_>> for DataType {
 
     fn try_from(desc: &TypeDesc) -> Result<Self> {
         let dt = match desc.name {
-            "Null" => DataType::Null,
+            "Null" | "NULL" => DataType::Null,
             "Boolean" => DataType::Boolean,
             "String" => DataType::String,
             "Int8" => DataType::Number(NumberDataType::Int8),
@@ -256,7 +256,7 @@ impl TryFrom<&Arc<ArrowField>> for Field {
                 )))
             }
         };
-        if f.is_nullable() {
+        if f.is_nullable() && !matches!(dt, DataType::Null) {
             dt = DataType::Nullable(Box::new(dt));
         }
         Ok(Field {

driver/tests/driver/select_simple.rs

@@ -22,6 +22,16 @@ async fn prepare() -> Box<dyn Connection> {
     new_connection(dsn).unwrap()
 }
 
+#[tokio::test]
+async fn select_null() {
+    let conn = prepare().await;
+    let row = conn.query_row("select null").await.unwrap();
+    assert!(row.is_some());
+    let row = row.unwrap();
+    let (val,): (Option<u8>,) = row.try_into().unwrap();
+    assert_eq!(val, None);
+}
+
 #[tokio::test]
 async fn select_string() {
     let conn = prepare().await;
@@ -109,7 +119,7 @@ async fn select_datetime() {
 }
 
 #[tokio::test]
-async fn select_null() {
+async fn select_nullable() {
     let conn = prepare().await;
     let row = conn
         .query_row("select sum(number) from numbers(0)")

tests/Makefile

@@ -1,5 +1,7 @@
 default: run
 
+run: test-core test-driver test-bendsql down
+
 prepare:
 	mkdir -p data/databend
 
@@ -19,8 +21,6 @@ test-bendsql: up
 	cd .. && ./cli/test.sh http
 	cd .. && ./cli/test.sh flight
 
-run: test-core test-driver test-bendsql
-
 down:
 	docker compose down