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85 lines
2.8 KiB
C++
85 lines
2.8 KiB
C++
#include <Functions/IFunctionImpl.h>
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#include <Functions/FunctionHelpers.h>
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#include <Functions/FunctionFactory.h>
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#include <DataTypes/DataTypesNumber.h>
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#include <DataTypes/DataTypeNullable.h>
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#include <Core/ColumnNumbers.h>
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#include <Columns/ColumnNullable.h>
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namespace DB
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{
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/// Implements the function nullIf which takes 2 arguments and returns
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/// NULL if both arguments have the same value. Otherwise it returns the
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/// value of the first argument.
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class FunctionNullIf : public IFunction
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{
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private:
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const Context & context;
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public:
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static constexpr auto name = "nullIf";
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static FunctionPtr create(const Context & context)
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{
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return std::make_shared<FunctionNullIf>(context);
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}
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explicit FunctionNullIf(const Context & context_) : context(context_) {}
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std::string getName() const override
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{
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return name;
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}
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size_t getNumberOfArguments() const override { return 2; }
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bool useDefaultImplementationForNulls() const override { return false; }
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bool useDefaultImplementationForConstants() const override { return true; }
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DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
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{
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return makeNullable(arguments[0]);
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}
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void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) override
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{
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/// nullIf(col1, col2) == if(col1 = col2, NULL, col1)
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Block temp_block = block;
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auto equals_func = FunctionFactory::instance().get("equals", context)->build(
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{temp_block.getByPosition(arguments[0]), temp_block.getByPosition(arguments[1])});
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size_t equals_res_pos = temp_block.columns();
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temp_block.insert({nullptr, equals_func->getReturnType(), ""});
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equals_func->execute(temp_block, {arguments[0], arguments[1]}, equals_res_pos, input_rows_count);
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/// Argument corresponding to the NULL value.
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size_t null_pos = temp_block.columns();
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/// Append a NULL column.
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ColumnWithTypeAndName null_elem;
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null_elem.type = block.getByPosition(result).type;
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null_elem.column = null_elem.type->createColumnConstWithDefaultValue(input_rows_count);
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null_elem.name = "NULL";
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temp_block.insert(null_elem);
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auto func_if = FunctionFactory::instance().get("if", context)->build(
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{temp_block.getByPosition(equals_res_pos), temp_block.getByPosition(null_pos), temp_block.getByPosition(arguments[0])});
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func_if->execute(temp_block, {equals_res_pos, null_pos, arguments[0]}, result, input_rows_count);
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block.getByPosition(result).column = makeNullable(std::move(temp_block.getByPosition(result).column));
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}
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};
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void registerFunctionNullIf(FunctionFactory & factory)
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{
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factory.registerFunction<FunctionNullIf>(FunctionFactory::CaseInsensitive);
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}
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}
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