// decompose splits an aggregate function to two parts: a final mode function and a partial mode function. Currently
// there are no differences between partial mode and complete mode, so we can confuse them.
func (a *aggPushDownSolver) decompose(aggFunc expression.AggregationFunction, schema expression.Schema, id string) ([]expression.AggregationFunction, expression.Schema) {
// Result is a slice because avg should be decomposed to sum and count. Currently we don't process this case.
result := []expression.AggregationFunction{aggFunc.Clone()}
for _, aggFunc := range result {
schema = append(schema, &expression.Column{
ColName: model.NewCIStr(fmt.Sprintf("join_agg_%d", len(schema))), // useless but for debug
FromID: id,
Position: len(schema),
RetType: aggFunc.GetType(),
})
}
aggFunc.SetArgs(expression.Schema2Exprs(schema[len(schema)-len(result):]))
aggFunc.SetMode(expression.FinalMode)
return result, schema
}
