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