Example #1
0
// isDecomposable checks if an aggregate function is decomposable. An aggregation function $F$ is decomposable
// if there exist aggregation functions F_1 and F_2 such that F(S_1 union all S_2) = F_2(F_1(S_1),F_1(S_2)),
// where S_1 and S_2 are two sets of values. We call S_1 and S_2 partial groups.
// It's easy to see that max, min, first row is decomposable, no matter whether it's distinct, but sum(distinct) and
// count(distinct) is not.
// Currently we don't support avg and concat.
func (a *aggPushDownSolver) isDecomposable(fun expression.AggregationFunction) bool {
	switch fun.GetName() {
	case ast.AggFuncAvg, ast.AggFuncGroupConcat:
		// TODO: Support avg push down.
		return false
	case ast.AggFuncMax, ast.AggFuncMin, ast.AggFuncFirstRow:
		return true
	case ast.AggFuncSum, ast.AggFuncCount:
		return !fun.IsDistinct()
	default:
		return false
	}
}