refactor: refine cast variant to map (#16691)

* refactor: refine cast variant to map * fix * address comment

Author: andylokandy

src/query/expression/src/evaluator.rs

@@ -43,6 +43,7 @@ use crate::types::BooleanType;
 use crate::types::DataType;
 use crate::types::NullableType;
 use crate::types::NumberScalar;
+use crate::types::StringType;
 use crate::types::VariantType;
 use crate::values::Column;
 use crate::values::ColumnBuilder;
@@ -640,7 +641,7 @@ impl<'a> Evaluator<'a> {
  ]))))
  }
  Value::Column(Column::Variant(col)) => {
- let mut key_builder = StringColumnBuilder::with_capacity(0, 0);
+ let mut key_builder = StringType::create_builder(col.len(), &[]);
  let mut value_builder =
  ArrayType::<VariantType>::create_builder(col.len(), &[]);
 
@@ -662,38 +663,32 @@ impl<'a> Evaluator<'a> {
  v.write_to_vec(&mut value_builder.builder.data);
  value_builder.builder.commit_row();
  }
+
  value_builder.commit_row();
  }
- let key_column = Column::String(key_builder.build());
 
- let value_column = value_builder.build();
- let validity = validity.map(|validity| {
- let mut inner_validity = MutableBitmap::with_capacity(col.len());
- for (index, offsets) in value_column.offsets.windows(2).enumerate() {
- inner_validity.extend_constant(
- (offsets[1] - offsets[0]) as usize,
- validity.get_bit(index),
- );
- }
- inner_validity.into()
- });
+ let key_col = Column::String(key_builder.build());
+ let value_col = Column::Array(Box::new(value_builder.build().upcast()));
 
- let new_value_column = self
+ let value_col = self
  .run_cast(
  span,
- &DataType::Variant,
+ &DataType::Array(Box::new(DataType::Variant)),
  &fields_dest_ty[1],
- Value::Column(Column::Variant(value_column.values)),
+ Value::Column(value_col),
  validity,
  options,
  )?
  .into_column()
+ .unwrap()
+ .into_array()
  .unwrap();
 
- let kv_column = Column::Tuple(vec![key_column, new_value_column]);
+ let kv_col = Column::Tuple(vec![key_col, value_col.values]);
+
  Ok(Value::Column(Column::Map(Box::new(ArrayColumn {
- values: kv_column,
- offsets: col.offsets,
+ values: kv_col,
+ offsets: value_col.offsets,
  }))))
  }
  other => unreachable!("source: {}", other),