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