1#include <Functions/IFunctionImpl.h>
2#include <Functions/FunctionHelpers.h>
3#include <Functions/FunctionFactory.h>
4#include <DataTypes/DataTypesNumber.h>
5#include <DataTypes/DataTypeNullable.h>
6#include <Core/ColumnNumbers.h>
7#include <Columns/ColumnNullable.h>
8
9
10namespace DB
11{
12
13/// Implements the function nullIf which takes 2 arguments and returns
14/// NULL if both arguments have the same value. Otherwise it returns the
15/// value of the first argument.
16class FunctionNullIf : public IFunction
17{
18private:
19 const Context & context;
20public:
21 static constexpr auto name = "nullIf";
22
23 static FunctionPtr create(const Context & context)
24 {
25 return std::make_shared<FunctionNullIf>(context);
26 }
27
28 FunctionNullIf(const Context & context_) : context(context_) {}
29
30 std::string getName() const override
31 {
32 return name;
33 }
34
35 size_t getNumberOfArguments() const override { return 2; }
36 bool useDefaultImplementationForNulls() const override { return false; }
37 bool useDefaultImplementationForConstants() const override { return true; }
38
39 DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
40 {
41 return makeNullable(arguments[0]);
42 }
43
44 void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) override
45 {
46 /// nullIf(col1, col2) == if(col1 = col2, NULL, col1)
47
48 Block temp_block = block;
49
50 auto equals_func = FunctionFactory::instance().get("equals", context)->build(
51 {temp_block.getByPosition(arguments[0]), temp_block.getByPosition(arguments[1])});
52
53 size_t equals_res_pos = temp_block.columns();
54 temp_block.insert({nullptr, equals_func->getReturnType(), ""});
55
56 equals_func->execute(temp_block, {arguments[0], arguments[1]}, equals_res_pos, input_rows_count);
57
58 /// Argument corresponding to the NULL value.
59 size_t null_pos = temp_block.columns();
60
61 /// Append a NULL column.
62 ColumnWithTypeAndName null_elem;
63 null_elem.type = block.getByPosition(result).type;
64 null_elem.column = null_elem.type->createColumnConstWithDefaultValue(input_rows_count);
65 null_elem.name = "NULL";
66
67 temp_block.insert(null_elem);
68
69 auto func_if = FunctionFactory::instance().get("if", context)->build(
70 {temp_block.getByPosition(equals_res_pos), temp_block.getByPosition(null_pos), temp_block.getByPosition(arguments[0])});
71 func_if->execute(temp_block, {equals_res_pos, null_pos, arguments[0]}, result, input_rows_count);
72
73 block.getByPosition(result).column = makeNullable(std::move(temp_block.getByPosition(result).column));
74 }
75};
76
77
78void registerFunctionNullIf(FunctionFactory & factory)
79{
80 factory.registerFunction<FunctionNullIf>(FunctionFactory::CaseInsensitive);
81}
82
83}
84
85