ClickHouse/dbms/include/DB/Functions/Conditional/NullMapBuilder.h

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#pragma once
#include <DB/Core/Block.h>
namespace DB
{
namespace Conditional
{
/// Here is provided a way to incrementally build the null map of the result column
/// of a multiIf invokation if its type is nullable.
class NullMapBuilder final
{
public:
/// Create a dummy builder when we don't need any builder, i.e. when the result
/// of multiIf is not nullable.
NullMapBuilder()
: block{empty_block}
{
}
/// This constructor takes the block that contains the original data received
/// by multiIf, i.e. they have not been processed.
NullMapBuilder(Block & block_)
: block{block_}, row_count{block.rows()}
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{
}
/// Check whether the builder is dummy or not.
operator bool() const { return block; }
bool operator!() const { return !block; }
/// Initialize the builder. For the non-trivial execution paths of multiIf.
void init(const ColumnNumbers & args);
/// Update the null map being built at the row that has just been processed
/// by multiIf. The parameter index indicates the index of the column being
/// checked for nullity. For non-trivial execution paths of multiIf.
void update(size_t index, size_t row);
/// Build the null map. The parameter index has the same meaning as above.
/// For the trivial execution path of multiIf.
void build(size_t index);
/// Accessor needed to return the fully built null map.
ColumnPtr getNullMap() const { return null_map; }
private:
/// Property of a column.
enum Property
{
/// Neither nullable nor null.
IS_ORDINARY = 0,
/// Nullable column.
IS_NULLABLE,
/// Null column.
IS_NULL
};
private:
Block & block;
/// Remember for each column representing an argument whether it is
/// nullable, null, or neither of them. This avoids us many costly
/// calls to virtual functions.
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PaddedPODArray<Property> cols_properties;
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ColumnPtr null_map;
size_t row_count;
private:
static Block empty_block;
};
}
}