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50 lines
1.3 KiB
C++
50 lines
1.3 KiB
C++
#include <Processors/ISimpleTransform.h>
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#include <Core/ColumnNumbers.h>
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namespace DB
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{
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/** Convert one block structure to another:
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*
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* Leaves only necessary columns;
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*
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* Columns are searched in source first by name;
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* and if there is no column with same name, then by position.
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*
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* Converting types of matching columns (with CAST function).
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*
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* Materializing columns which are const in source and non-const in result,
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* throw if they are const in result and non const in source,
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* or if they are const and have different values.
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*/
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class ConvertingTransform : public ISimpleTransform
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{
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public:
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enum class MatchColumnsMode
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{
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/// Require same number of columns in source and result. Match columns by corresponding positions, regardless to names.
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Position,
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/// Find columns in source by their names. Allow excessive columns in source.
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Name,
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};
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ConvertingTransform(
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Block source_header_,
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Block result_header_,
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MatchColumnsMode mode_,
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const Context & context_);
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String getName() const override { return "Converting"; }
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protected:
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void transform(Chunk & chunk) override;
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private:
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const Context & context;
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/// How to construct result block. Position in source block, where to get each column.
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ColumnNumbers conversion;
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};
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}
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