THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Here the AnyType class works for both passing data from the DBMS to the C++ function, as well as returning values back from C++. Refer to TypeTraits_impl.hpp for more details.
Transition function
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AnyType
avg_var_transition::run(AnyType& args) {
// get current state value
AvgVarTransitionState<MutableArrayHandle<double> > state = args[0];
// get current row value
double x = args[1].getAs<double>();
double d = (x - state.avg);
// online update mean
state.avg += d / static_cast<double>(state.numRows + 1);
double new_d = (x - state.avg);
double a = static_cast<double>(state.numRows) / static_cast<double>(state.numRows + 1);
// online update variance
state.var = state.var * a + d * new_d / static_cast<double>(state.numRows + 1);
state.numRows ++;
return state;
} |
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- Again: the arguments contained in
AnyType& argsare defined inavg_var.sql_in. - The details are hidden in the method of class
AvgVarTransitionStatewhich overloads the operator+=
Final function
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AnyType
avg_var_final::run(AnyType& args) {
AvgVarTransitionState<MutableArrayHandle<double> > state = args[0];
// If we haven't seen any data, just return Null. This is the standard
// behavior of aggregate function on empty data sets (compare, e.g.,
// how PostgreSQL handles sum or avg on empty inputs)
if (state.numRows == 0)
return Null();
return state;
} |
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