ClickHouse

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#include <Functions/IFunction.h>
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#include <Functions/FunctionFactory.h>
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#include <DataTypes/DataTypeString.h>
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#include <Core/Field.h>
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namespace DB
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{
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namespace
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{
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/// Returns name of IColumn instance.
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class FunctionToColumnTypeName : public IFunction
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{
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public:
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    static constexpr auto name = "toColumnTypeName";
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    static FunctionPtr create(ContextPtr)
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    {
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        return std::make_shared<FunctionToColumnTypeName>();
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    }
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    String getName() const override
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    {
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        return name;
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    }
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    bool useDefaultImplementationForNulls() const override { return false; }
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    bool useDefaultImplementationForNothing() const override { return false; }
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    bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }
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    bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
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    size_t getNumberOfArguments() const override
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    {
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        return 1;
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    }
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    DataTypePtr getReturnTypeImpl(const DataTypes & /*arguments*/) const override
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    {
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        return std::make_shared<DataTypeString>();
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    }
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    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
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    {
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        return DataTypeString().createColumnConst(input_rows_count, arguments[0].column->getName());
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    }
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    ColumnPtr getConstantResultForNonConstArguments(const ColumnsWithTypeAndName & arguments, const DataTypePtr &) const override
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    {
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        return DataTypeString().createColumnConst(1, arguments[0].type->createColumn()->getName());
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    }
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};
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}
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REGISTER_FUNCTION(ToColumnTypeName)
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{
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    factory.registerFunction<FunctionToColumnTypeName>();
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}
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}
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