Aggregate NULLs

All-NULL SUM Gives NULL

A bucket with no present integer cells returns NULL.

highlighted = computed this step

All-NULL SUM

If SUM finds no present integer cell, this track's SQL precedent returns NULL.

all NULL sum\text{all NULL sum}

Read the all-NULL bucket

The bucket has 2 rows, 0 present quantity cells, and SUM NULL.

SUM is NULL\text{SUM is NULL}

Aggregate NULL examples are tiny finite table transforms; SQL dialect completeness, optimizer behavior, indexing, product behavior, and performance claims are out of scope.

All-NULL SUM gives NULL: base rowsidqty1NULL2NULL Group bucketskeysourceRowsrowCount[all_rows][0, 1]2 Aggregate resultskeysourceRowsaggregates[all_rows][0, 1]{rows_seen:2, qty_seen:0, qty_sum:NULL} NULL-skip detailskeyaggregateseencounted/addednullSkippedresult[all_rows]rows_seen2202[all_rows]qty_seen2020[all_rows]qty_sum202NULL Output rowsrows_seenqty_seenqty_sum20NULL Aggregate NULL factsfactvalueinputRowCount2groupCount1aggregateCount3outputRowCount1countStarCountsEveryRowyescountColumnSkipsNullyessumSkipsNullyesallNullSumGivesNULLgroupOrderfirst_seen_input_orderoutputOrderdeterministic_group_order

No made-up zero

The result is NULL because no non-NULL integer was available to add.

no present cell\text{no present cell}

Summary

All-NULL SUM is shown explicitly instead of hidden.

NULL result visible\text{NULL result visible}