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93 lines
2.7 KiB
C++
93 lines
2.7 KiB
C++
#include <Functions/IFunctionImpl.h>
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#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionHelpers.h>
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#include <DataTypes/DataTypesNumber.h>
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#include <DataTypes/DataTypeString.h>
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#include <Columns/ColumnString.h>
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#include <Columns/ColumnConst.h>
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#include <Core/Field.h>
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#include <unordered_map>
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#include <Poco/String.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 BAD_ARGUMENTS;
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}
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namespace
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{
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/** globalVariable('name') - takes constant string argument and returns the value of global variable with that name.
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* It is intended for compatibility with MySQL.
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*
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* Currently it's a stub, no variables are implemented. Feel free to add more variables.
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*/
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class FunctionGlobalVariable : public IFunction
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{
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public:
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static constexpr auto name = "globalVariable";
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static FunctionPtr create(const Context &)
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{
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return std::make_shared<FunctionGlobalVariable>();
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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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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 ColumnsWithTypeAndName & arguments) const override
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{
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if (!checkColumnConst<ColumnString>(arguments[0].column.get()))
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throw Exception("Argument of function " + getName() + " must be constant string", ErrorCodes::BAD_ARGUMENTS);
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String variable_name = assert_cast<const ColumnConst &>(*arguments[0].column).getValue<String>();
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auto variable = global_variable_map.find(Poco::toLower(variable_name));
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if (variable == global_variable_map.end())
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return std::make_shared<DataTypeInt32>();
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else
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return variable->second.type;
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}
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ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const override
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{
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const ColumnWithTypeAndName & col = arguments[0];
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String variable_name = assert_cast<const ColumnConst &>(*col.column).getValue<String>();
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auto variable = global_variable_map.find(Poco::toLower(variable_name));
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Field val = 0;
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if (variable != global_variable_map.end())
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val = variable->second.value;
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return result_type->createColumnConst(input_rows_count, val);
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}
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private:
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struct TypeAndValue
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{
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DataTypePtr type;
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Field value;
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};
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std::unordered_map<String, TypeAndValue> global_variable_map = {
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{"max_allowed_packet", {std::make_shared<DataTypeInt32>(), 67108864}}, {"version", {std::make_shared<DataTypeString>(), "5.7.30"}}};
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};
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}
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void registerFunctionGlobalVariable(FunctionFactory & factory)
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{
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factory.registerFunction<FunctionGlobalVariable>();
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}
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}
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