allow converting from DateTime2 to Datetimen in 'tds73'

Author: Geo W

src/tds/codec/column_data.rs

@@ -594,6 +594,20 @@ impl<'a> Encode<BytesMutWithTypeInfo<'a>> for ColumnData<'a> {
                 time.encode(&mut *dst)?;
             }
             #[cfg(feature = "tds73")]
+            (ColumnData::DateTime2(opt), Some(TypeInfo::VarLenSized(vlc)))
+                if vlc.r#type() == VarLenType::Datetimen =>
+            {
+                if let Some(dt2) = opt {
+                    dst.put_u8(8);
+                    let days = dt2.date().days() - 693595; // minus days gap between year 1 and year 1900;
+                    let seconds_fragments = dt2.time().increments() * 100 * 300 / 1e9 as u64; // degrade second's precision
+                    dst.put_u32_le(days as u32);
+                    dst.put_u32_le(seconds_fragments as u32);
+                } else {
+                    dst.put_u8(0);
+                }
+            }
+            #[cfg(feature = "tds73")]
             (ColumnData::DateTime2(opt), Some(TypeInfo::VarLenSized(vlc)))
                 if vlc.r#type() == VarLenType::Datetime2 =>
             {