ClickHouse/src/Functions/globalVariable.cpp
2020-07-21 16:58:07 +03:00

92 lines
2.7 KiB
C++

#include <Functions/IFunctionImpl.h>
#include <Functions/FunctionFactory.h>
#include <Functions/FunctionHelpers.h>
#include <DataTypes/DataTypesNumber.h>
#include <DataTypes/DataTypeString.h>
#include <Columns/ColumnString.h>
#include <Columns/ColumnConst.h>
#include <Core/Field.h>
#include <unordered_map>
#include <Poco/String.h>
namespace DB
{
namespace ErrorCodes
{
extern const int BAD_ARGUMENTS;
}
/** globalVariable('name') - takes constant string argument and returns the value of global variable with that name.
* It is intended for compatibility with MySQL.
*
* Currently it's a stub, no variables are implemented. Feel free to add more variables.
*/
class FunctionGlobalVariable : public IFunction
{
public:
static constexpr auto name = "globalVariable";
static FunctionPtr create(const Context &)
{
return std::make_shared<FunctionGlobalVariable>();
}
String getName() const override
{
return name;
}
size_t getNumberOfArguments() const override
{
return 1;
}
DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
{
if (!checkColumnConst<ColumnString>(arguments[0].column.get()))
throw Exception("Argument of function " + getName() + " must be constant string", ErrorCodes::BAD_ARGUMENTS);
String variable_name = assert_cast<const ColumnConst &>(*arguments[0].column).getValue<String>();
auto variable = global_variable_map.find(Poco::toLower(variable_name));
if (variable == global_variable_map.end())
return std::make_shared<DataTypeInt32>();
else
return variable->second.type;
}
void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) const override
{
const ColumnWithTypeAndName & col = block.getByPosition(arguments[0]);
String variable_name = assert_cast<const ColumnConst &>(*col.column).getValue<String>();
auto variable = global_variable_map.find(Poco::toLower(variable_name));
Field val = 0;
if (variable != global_variable_map.end())
val = variable->second.value;
auto & result_col = block.getByPosition(result);
result_col.column = result_col.type->createColumnConst(input_rows_count, val);
}
private:
struct TypeAndValue
{
DataTypePtr type;
Field value;
};
std::unordered_map<String, TypeAndValue> global_variable_map = {
{"max_allowed_packet", {std::make_shared<DataTypeInt32>(), 67108864}}, {"version", {std::make_shared<DataTypeString>(), "5.7.30"}}};
};
void registerFunctionGlobalVariable(FunctionFactory & factory)
{
factory.registerFunction<FunctionGlobalVariable>();
}
}