#include <Functions/IFunction.h> #include <Functions/FunctionFactory.h> #include <Core/Field.h> #include <Columns/ColumnConst.h> #include <DataTypes/DataTypeFactory.h> namespace DB { namespace ErrorCodes { extern const int ILLEGAL_COLUMN; } namespace { /// Returns global default value for type name (example: 0 for numeric types, '' for String). class FunctionDefaultValueOfTypeName : public IFunction { public: static constexpr auto name = "defaultValueOfTypeName"; static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionDefaultValueOfTypeName>(); } String getName() const override { return name; } bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; } bool useDefaultImplementationForNulls() const override { return false; } bool useDefaultImplementationForLowCardinalityColumns() const override { return false; } size_t getNumberOfArguments() const override { return 1; } DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override { const ColumnConst * col_type_const = typeid_cast<const ColumnConst *>(arguments.front().column.get()); if (!col_type_const || !isString(arguments.front().type)) throw Exception(ErrorCodes::ILLEGAL_COLUMN, "The argument of function {} must be a constant string describing type.", getName()); return DataTypeFactory::instance().get(col_type_const->getValue<String>()); } ColumnPtr executeImpl(const ColumnsWithTypeAndName &, const DataTypePtr & result_type, size_t input_rows_count) const override { const IDataType & type = *result_type; return type.createColumnConst(input_rows_count, type.getDefault()); } }; } REGISTER_FUNCTION(DefaultValueOfTypeName) { factory.registerFunction<FunctionDefaultValueOfTypeName>(); } }