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#include <Functions/IFunction.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;
}
namespace
{
/** 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(ContextPtr)
{
return std::make_shared<FunctionGlobalVariable>();
}
String getName() const override
{
return name;
}
size_t getNumberOfArguments() const override
{
return 1;
}
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
{
if (!checkColumnConst<ColumnString>(arguments[0].column.get()))
throw Exception(ErrorCodes::BAD_ARGUMENTS, "Argument of function {} must be constant string", getName());
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;
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const override
{
const ColumnWithTypeAndName & col = 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;
return result_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"}},
{"version_comment", {std::make_shared<DataTypeString>(), ""}},
{"transaction_isolation", {std::make_shared<DataTypeString>(), "READ-UNCOMMITTED"}}};
};
}
REGISTER_FUNCTION(GlobalVariable)
{
factory.registerFunction<FunctionGlobalVariable>();
}
}
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