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69 lines
2.0 KiB
C++
69 lines
2.0 KiB
C++
#include <Functions/IFunction.h>
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#include <Functions/FunctionFactory.h>
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#include <DataTypes/DataTypesNumber.h>
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namespace DB
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{
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/** The `indexHint` function takes any number of any arguments and always returns one.
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*
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* This function has a special meaning (see ExpressionAnalyzer, KeyCondition)
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* - the expressions inside it are not evaluated;
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* - but when analyzing the index (selecting ranges for reading), this function is treated the same way,
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* as if instead of using it the expression itself would be.
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*
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* Example: WHERE something AND indexHint(CounterID = 34)
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* - do not read or calculate CounterID = 34, but select ranges in which the CounterID = 34 expression can be true.
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*
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* The function can be used for debugging purposes, as well as for (hidden from the user) query conversions.
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*/
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class FunctionIndexHint : public IFunction
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{
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public:
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static constexpr auto name = "indexHint";
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static FunctionPtr create(ContextPtr)
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{
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return std::make_shared<FunctionIndexHint>();
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}
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bool isVariadic() const override
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{
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return true;
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}
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size_t getNumberOfArguments() const override
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{
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return 0;
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}
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bool useDefaultImplementationForNulls() const override { return false; }
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bool isSuitableForConstantFolding() const override { return false; }
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bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
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String getName() const override
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{
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return name;
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}
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DataTypePtr getReturnTypeImpl(const DataTypes & /*arguments*/) const override
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{
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return std::make_shared<DataTypeUInt8>();
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}
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ColumnPtr executeImpl(const ColumnsWithTypeAndName &, const DataTypePtr &, size_t input_rows_count) const override
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{
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return DataTypeUInt8().createColumnConst(input_rows_count, 1u);
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}
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};
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void registerFunctionIndexHint(FunctionFactory & factory)
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{
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factory.registerFunction<FunctionIndexHint>();
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}
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}
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