1#include <Functions/IFunctionImpl.h>
2#include <Functions/FunctionFactory.h>
3#include <DataTypes/DataTypeLowCardinality.h>
4#include <Columns/ColumnLowCardinality.h>
5#include <Common/typeid_cast.h>
6
7
8namespace DB
9{
10
11namespace ErrorCodes
12{
13 extern const int ILLEGAL_TYPE_OF_ARGUMENT;
14}
15
16
17class FunctionLowCardinalityKeys: public IFunction
18{
19public:
20 static constexpr auto name = "lowCardinalityKeys";
21 static FunctionPtr create(const Context &) { return std::make_shared<FunctionLowCardinalityKeys>(); }
22
23 String getName() const override { return name; }
24
25 size_t getNumberOfArguments() const override { return 1; }
26
27 bool useDefaultImplementationForNulls() const override { return false; }
28 bool useDefaultImplementationForConstants() const override { return true; }
29 bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }
30
31 DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
32 {
33 auto * type = typeid_cast<const DataTypeLowCardinality *>(arguments[0].get());
34 if (!type)
35 throw Exception("First first argument of function lowCardinalityKeys must be ColumnLowCardinality, but got"
36 + arguments[0]->getName(), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
37
38 return type->getDictionaryType();
39 }
40
41 void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t /*input_rows_count*/) override
42 {
43 auto arg_num = arguments[0];
44 const auto & arg = block.getByPosition(arg_num);
45 auto & res = block.getByPosition(result);
46 const auto * low_cardinality_column = typeid_cast<const ColumnLowCardinality *>(arg.column.get());
47 res.column = low_cardinality_column->getDictionary().getNestedColumn()->cloneResized(arg.column->size());
48 }
49};
50
51
52void registerFunctionLowCardinalityKeys(FunctionFactory & factory)
53{
54 factory.registerFunction<FunctionLowCardinalityKeys>();
55}
56
57}
58