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dbms: better [#METR-19266]

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This commit is contained in:
Alexey Arno 2016-08-25 16:23:24 +03:00
parent d4da820f6c
commit ae2d8d9adb
1 changed files with 19 additions and 51 deletions
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64
dbms/include/DB/DataStreams/NullableAdapterBlockInputStream.h
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@ -13,9 +13,7 @@ namespace DB
/// - if a target column is nullable while the corresponding source
/// column is not, we embed the source column into a nullable column;
/// - if a source column is nullable while the corresponding target
/// column is not, we extract the nested column from the source.
/// Moreover all the NULL values are replaced by the default value
/// for the nested column;
/// column is not, we extract the nested column from the source;
/// - otherwise we just perform an identity mapping.
class NullableAdapterBlockInputStream : public IProfilingBlockInputStream
{
@ -26,7 +24,7 @@ private:
{
/// Do nothing.
NONE = 0,
/// Convert nullable column to ordinary column. Convert NULLs to default values.
/// Convert nullable column to ordinary column.
TO_ORDINARY,
/// Convert non-nullable column to nullable column.
TO_NULLABLE
@ -71,63 +69,33 @@ protected:
if (actions[i] == TO_ORDINARY)
{
const auto & nullable_col = static_cast<const ColumnNullable &>(*elem.column);
const auto & nested_col = *nullable_col.getNestedColumn();
const auto & nullable_type = static_cast<const DataTypeNullable &>(*elem.type);
const auto & null_map = static_cast<const ColumnUInt8 &>(*nullable_col.getNullValuesByteMap()).getData();
bool has_nulls = std::any_of(null_map.begin(), null_map.end(), [](UInt8 val){ return val == 1; });
if (has_nulls)
{
/// Slow path: since we have NULL values that must be replaced,
/// we have to build a new column.
ColumnPtr new_col_holder = nullable_col.getNestedColumn()->cloneEmpty();
IColumn & new_col = *new_col_holder;
new_col.reserve(nullable_col.size());
for (size_t i = 0; i < nullable_col.size(); ++i)
{
if (nullable_col.isNullAt(i))
new_col.insertDefault();
else
new_col.insertFrom(nested_col, i);
}
new_elem =
{
new_col_holder,
nullable_type.getNestedType(),
elem.name
};
}
else
{
/// Fast path: there are no NULL values.
/// Just return the nested column.
new_elem =
{
/// For performance reasons, if the source column contains a NULL,
/// we follow a non-strict approach. We rely on the fact that most
/// users will write something such as:
///
/// INSERT INTO foo(col) SELECT col FROM bar WHERE col IS NOT NULL
///
/// If required, in a future release we could add a server parameter
/// so that customers would be able to decide whether inserting
/// a NULL value into an non-nullable column is semantically correct
/// or not.
res.insert({
nullable_col.getNestedColumn(),
nullable_type.getNestedType(),
elem.name
};
}
res.insert(new_elem);
});
}
else if (actions[i] == TO_NULLABLE)
{
auto null_map = std::make_shared<ColumnUInt8>(elem.column->size(), 0);
ColumnWithTypeAndName new_elem
{
res.insert({
std::make_shared<ColumnNullable>(elem.column, null_map),
std::make_shared<DataTypeNullable>(elem.type),
elem.name
};
res.insert(new_elem);
});
}
else if (actions[i] == NONE)
res.insert(elem);