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Use CalcSums to aggregate filtered sets
Contributions welcome — open a PR to refine or extend this article.
Description
When the task is to compute a sum over a filtered set, CalcSums lets the platform push the aggregation down to SQL using SIFT indexes. Iterating rows in AL to accumulate a total transports every row's data to the runtime only to discard it after adding one field. On ledger-entry-scale tables this difference is dramatic. The same SIFT infrastructure backs Sum-style FlowFields; when the value you need is already declared as a FlowField, calling CalcSums on the underlying table with the correct filters produces the same aggregate.
Best Practice
Set the required filters on the record, then call CalcSums on the field you want aggregated. Ensure the table has a key whose SumIndexFields includes the summed field and whose key prefix matches the filters (see add-sift-keys-for-flowfields).
See sample: use-calcsums-for-flowfield-totals.good.al.
Anti Pattern
Looping a filtered set with FindSet and adding a field to an accumulator on every iteration performs work in AL that SQL already knows how to do in one aggregate query.
See sample: use-calcsums-for-flowfield-totals.bad.al.