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68 lines
2.2 KiB
C++
68 lines
2.2 KiB
C++
#include <Functions/IFunction.h>
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#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionHelpers.h>
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namespace DB
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{
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namespace ErrorCodes
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{
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extern const int ILLEGAL_COLUMN;
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}
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namespace
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{
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class FunctionGetSubcolumn : public IFunction
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{
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public:
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static constexpr auto name = "getSubcolumn";
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static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionGetSubcolumn>(); }
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String getName() const override { return name; }
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size_t getNumberOfArguments() const override { return 2; }
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bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo &) const override { return true; }
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bool useDefaultImplementationForConstants() const override { return true; }
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ColumnNumbers getArgumentsThatAreAlwaysConstant() const override { return {1}; }
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DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
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{
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auto subcolumn_name = getSubcolumnName(arguments);
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return arguments[0].type->getSubcolumnType(subcolumn_name);
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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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auto subcolumn_name = getSubcolumnName(arguments);
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return arguments[0].type->getSubcolumn(subcolumn_name, arguments[0].column);
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}
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private:
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static std::string_view getSubcolumnName(const ColumnsWithTypeAndName & arguments)
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{
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const auto * column = arguments[1].column.get();
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if (!isString(arguments[1].type) || !column || !checkAndGetColumnConstStringOrFixedString(column))
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throw Exception(ErrorCodes::ILLEGAL_COLUMN,
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"The second argument of function {} should be a constant string with the name of a subcolumn", name);
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return column->getDataAt(0).toView();
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}
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};
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}
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REGISTER_FUNCTION(GetSubcolumn)
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{
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factory.registerFunction<FunctionGetSubcolumn>({
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R"(
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Receives the expression or identifier and constant string with the name of subcolumn.
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Returns requested subcolumn extracted from the expression.
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)",
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Documentation::Examples{{"getSubcolumn", "SELECT getSubcolumn(array_col, 'size0'), getSubcolumn(tuple_col, 'elem_name')"}},
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Documentation::Categories{"OtherFunctions"}
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});
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}
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}
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