fix(driver): parse null value for Nullable column

driver/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "databend-driver"
-version = "0.2.16"
+version = "0.2.17"
 edition = "2021"
 license = "Apache-2.0"
 description = "Databend Driver for Rust"

driver/src/value.rs

@@ -18,6 +18,7 @@ use crate::error::{ConvertError, Error, Result};
 
 // Thu 1970-01-01 is R.D. 719163
 const DAYS_FROM_CE: i32 = 719_163;
+const NULL_VALUE: &str = "NULL";
 
 #[cfg(feature = "flight-sql")]
 use {
@@ -140,7 +141,13 @@ impl TryFrom<(&DataType, &str)> for Value {
             DataType::Date => Ok(Self::Date(
                 chrono::NaiveDate::parse_from_str(v, "%Y-%m-%d")?.num_days_from_ce() - DAYS_FROM_CE,
             )),
-            DataType::Nullable(inner) => Self::try_from((inner.as_ref(), v)),
+            DataType::Nullable(inner) => {
+                if v == NULL_VALUE {
+                    Ok(Self::Null)
+                } else {
+                    Self::try_from((inner.as_ref(), v))
+                }
+            }
             // TODO:(everpcpc) handle complex types
             _ => Ok(Self::String(v.to_string())),
         }
@@ -153,6 +160,9 @@ impl TryFrom<(&ArrowField, &Arc<dyn ArrowArray>, usize)> for Value {
     fn try_from(
         (field, array, seq): (&ArrowField, &Arc<dyn ArrowArray>, usize),
     ) -> std::result::Result<Self, Self::Error> {
+        if field.is_nullable() && array.is_null(seq) {
+            return Ok(Value::Null);
+        }
         match field.data_type() {
             ArrowDataType::Null => Ok(Value::Null),
             ArrowDataType::Boolean => match array.as_any().downcast_ref::<BooleanArray>() {
@@ -361,6 +371,40 @@ impl TryFrom<Value> for NaiveDate {
     }
 }
 
+// This macro implements TryFrom to Option for Nullable column
+macro_rules! impl_try_from_to_option {
+    ($($t:ty),*) => {
+        $(
+            impl TryFrom<Value> for Option<$t> {
+                type Error = Error;
+                fn try_from(val: Value) -> Result<Self> {
+                    match val {
+                        Value::Null => Ok(None),
+                        _ => {
+                            let inner: $t = val.try_into()?;
+                            Ok(Some(inner))
+                        },
+                    }
+
+                }
+            }
+        )*
+    };
+}
+
+impl_try_from_to_option!(String);
+impl_try_from_to_option!(bool);
+impl_try_from_to_option!(u8);
+impl_try_from_to_option!(u16);
+impl_try_from_to_option!(u32);
+impl_try_from_to_option!(u64);
+impl_try_from_to_option!(i8);
+impl_try_from_to_option!(i16);
+impl_try_from_to_option!(i32);
+impl_try_from_to_option!(i64);
+impl_try_from_to_option!(f32);
+impl_try_from_to_option!(f64);
+
 impl std::fmt::Display for NumberValue {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {

driver/tests/driver/select_simple.rs

@@ -108,6 +108,32 @@ async fn select_datetime() {
     }
 }
 
+#[tokio::test]
+async fn select_null() {
+    let conn = prepare().await;
+    let row = conn
+        .query_row("select sum(number) from numbers(0)")
+        .await
+        .unwrap();
+    assert!(row.is_some());
+    let row = row.unwrap();
+    let (val,): (Option<u64>,) = row.try_into().unwrap();
+    assert_eq!(val, None);
+}
+
+#[tokio::test]
+async fn select_nullable_u64() {
+    let conn = prepare().await;
+    let row = conn
+        .query_row("select sum(number) from numbers(100)")
+        .await
+        .unwrap();
+    assert!(row.is_some());
+    let row = row.unwrap();
+    let (val,): (Option<u64>,) = row.try_into().unwrap();
+    assert_eq!(val, Some(4950));
+}
+
 // TODO:(everpcoc) parse to real array
 // #[tokio::test]
 // async fn select_array() {