fix(driver-sql): an all-NULL sum answers 0 on every face — fold at the aggregate door, conformance cell on every enrolled face (#15546) (#16720)

* fix(driver-sql): fold an all-NULL sum to 0 in the aggregate presentation, and pin it on every face

SQL SUM skips NULLs and answers NULL once it has skipped every row of a
group, so driver-sql answered null where the engine's in-memory tier,
driver-memory and driver-mongodb answer 0 and emptyGroupValueFor rules 0.
Measured null on better-sqlite3, live PostgreSQL 16.13 and live MySQL
8.0.46. Ruled option A on #15546 (maintainer, 2026-09-07): the SQL face
moves. The fold reads the identity from emptyGroupValueFor at the
aggregate door; the statement is unchanged.

The conformance fixture gains a nullable numeric column, amount, NULL in
every east row, and three cases pin the ruled answer on every enrolled
face; every harness that seeds the rows declares the column.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ADLdAs2pVcH17h9tZKWMBg

* test(conformance): keep a NULL aggregate answer as null in the SQL-family and in-memory harnesses

Number(null) is 0 — the ruled answer for the all-null sum cell — so the
unconditional Number(r.n) coercion made that cell green with the
driver-sql fold ablated (measured 85/85 green against a driver answering
null). The harnesses, not the faces, were holding the observable.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ADLdAs2pVcH17h9tZKWMBg

* fix(driver-turso): the remote transport folds an all-NULL sum to 0 like the local face

TursoDriver picks the remote compiler or SqlDriver's from url, so without
this the same driver answered the all-NULL sum 0 locally and null
remotely. Measured null on the enrolled remote face with a
null-preserving harness. Same fold, same policy read (#15546).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ADLdAs2pVcH17h9tZKWMBg

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: os-musk

.changeset/driver-sql-all-null-sum-folds-to-zero.md

@@ -0,0 +1,13 @@
+---
+"@objectstack/driver-sql": minor
+"@objectstack/driver-turso": minor
+"@objectstack/spec": minor
+---
+
+`SqlDriver.aggregate` answers `0` — not `null` — for a `sum` over a group whose aggregand is NULL in every row, matching the engine's in-memory aggregate tier and the identity `emptyGroupValueFor` already declares (#15546; maintainer ruling 2026-09-07, option A: a non-empty group whose aggregand is absent and an empty group are the SAME case for `sum`, and the SQL face is the one that moves).
+
+SQL `SUM` skips NULLs and answers NULL once it has skipped everything, so on every dialect this driver targets (measured on better-sqlite3, live PostgreSQL 16.13 and live MySQL 8.0.46) a grouped list view with a `sum` summary on a nullable number or currency column rendered a BLANK total for a group whose column was empty in every row — while the same view on a deployment whose query took the engine's in-memory path rendered `0`. Which path answered was decided by a driver capability bit the caller never sees. The fold is part of the driver's aggregate presentation (`foldEmptyAggregateAnswers`): the compiled statement is unchanged (no `COALESCE`), the answer is the JS number `0` on every dialect, and `avg`/`min`/`max` — which have no identity over nothing — still answer `null`. The identity is read from `emptyGroupValueFor` rather than restated, so the two faces cannot drift apart on it again.
+
+`@objectstack/driver-turso`: the REMOTE transport's `aggregate` carries the same fold (`RemoteTransport.foldEmptyAggregateAnswers`). `TursoDriver` picks the remote compiler or the local `SqlDriver` one from `url`, so without it the same driver would have answered the all-NULL `sum` as `0` locally and `null` remotely — one query, two answers, decided by a connection string, the seam the shared conformance table exists to close. Measured `null` on the enrolled remote face before the fold.
+
+`@objectstack/spec`: the aggregate-vocabulary conformance fixture gains a NULLABLE numeric column. `AggregationRow.amount` (`number | null`) is NULL in every row of the `east` group and in two of the four `west` rows, and `AGGREGATION_CASES` gains the three cases that pin the ruled answer on every enrolled face — `sum(amount)` grouped by region (`east` 0 / `west` 40), its `count(amount)` reachability control (`east` 0 / `west` 2, which is what proves the nulls were stored as nulls), and the ungrouped partial-null control (40). A harness that runs the table MUST declare `amount` as a nullable numeric column and seed its nulls AS nulls, exactly as it already must for `stage`; a `0` written in place of a null turns the cell green for the wrong reason.

packages/drivers/driver-sql/src/sql-driver-11635-boolean-aggregand-answers.test.ts

@@ -87,6 +87,9 @@ describe(`[#11635] driver-sql — boolean aggregands answer the ruled values (${
           region: { type: 'string' },
           stage: { type: 'string' },
           score: { type: 'number' },
+          // [#15546] The fixture rows carry a nullable `amount` too — declared
+          // so the verbatim seed below lands every column it carries.
+          amount: { type: 'number' },
           flag: { type: 'boolean' },
         },
       },

packages/drivers/driver-sql/src/sql-driver-aggregation-conformance.test.ts

@@ -179,6 +179,11 @@ const CONFORMANCE_OBJECT = {
     // Nullable, and it must stay that way — see `AggregationRow.stage`.
     stage: { type: 'text', name: 'stage' },
     score: { type: 'number', name: 'score' },
+    // [#15546] Nullable, and it must stay that way — see `AggregationRow.amount`:
+    // the `east` group is NULL in every row, which is the cell the ruled
+    // `sum` → `0` fold is pinned on. A `NOT NULL` column, or a `0` seeded in
+    // place of a null, turns that cell green for the wrong reason.
+    amount: { type: 'number', name: 'amount' },
     // [#11152] Declared `type: 'boolean'` on purpose — see `AggregationRow.flag`:
     // the ruled point of the boolean cases is that aggregation answers NUMBERS
     // (min=0/max=1) even where the declared type would present a row read as a
@@ -211,8 +216,14 @@ const actualFor = (c: AggregationCase, rows: Array<Record<string, unknown>>) =>
   // `groupByAlias ?? groupBy`. Reading `c.groupBy` unconditionally is the bug
   // this axis exists to catch: it is green on a face that ignores the alias.
   const groupKey = c.groupByAlias ?? c.groupBy;
+  // [#15546] A NULL answer is kept as `null`, never coerced: `Number(null)` is
+  // `0`, which is the ruled answer for the all-null `sum` cell — so the
+  // unconditional `Number(r.n)` this read as before made that cell green with
+  // the fold ABLATED (measured: 85/85 green against a driver answering
+  // `null`). The harness, not the driver, was holding the observable. The
+  // string-typed answers node-pg hands back (`"6"` for `COUNT`) still coerce.
   return rows
-    .map((r) => ({ group: groupKey ? String(r[groupKey]) : null, value: Number(r.n) }))
+    .map((r) => ({ group: groupKey ? String(r[groupKey]) : null, value: r.n === null ? null : Number(r.n) }))
     .sort((x, y) => String(x.group).localeCompare(String(y.group)));
 };
 
@@ -247,13 +258,18 @@ describe(`[#6409] SqlDriver — aggregate vocabulary conformance (${cell.label})
     expect(rows.map((r: any) => String(r.id))).toEqual(['1', '2', '3', '4', '5', '6']);
     for (const r of rows as any[]) {
       const seeded = AGGREGATION_ROWS.find((s) => s.id === String(r.id))!;
-      expect([r.region, r.stage ?? null, Number(r.score)], r.id)
-        .toEqual([seeded.region, seeded.stage, seeded.score]);
+      expect([r.region, r.stage ?? null, Number(r.score), r.amount ?? null], r.id)
+        .toEqual([seeded.region, seeded.stage, seeded.score, seeded.amount]);
     }
     // The property the null cases hang off, asserted directly: an empty string
     // in place of a null would keep every `count_distinct` case green at the
     // wrong number.
     expect((rows as any[]).filter((r) => r.stage === null)).toHaveLength(2);
+    // [#15546] The property the all-null `sum` cell hangs off: four NULL
+    // amounts, both `east` rows among them. A `0` seeded in place of a null
+    // answers the ruled `0` without the fold ever running.
+    expect((rows as any[]).filter((r) => r.amount === null), 'null amounts').toHaveLength(4);
+    expect((rows as any[]).filter((r) => r.region === 'east' && r.amount === null), 'east all-null').toHaveLength(2);
     // [#11152] The property the boolean cases hang off: 3 true / 3 false. A
     // seed that folded the flags turns every boolean case into a test of the
     // wrong table. `Boolean(...)` because the ROW read is presentation-shaped

packages/drivers/driver-sql/src/sql-driver.ts

@@ -20,7 +20,7 @@ import { parseAutonumberFormat, renderAutonumber, resolveAutonumberFormat, readA
 // The DECLARED aggregate vocabulary (#5907). Read from the spec so this driver's
 // "the protocol has no such function" refusal cannot drift from what
 // `AggregationNodeSchema.function` actually admits.
-import { AggregationFunction } from '@objectstack/spec/data';
+import { AggregationFunction, emptyGroupValueFor } from '@objectstack/spec/data';
 import { STRUCTURED_JSON_TYPES, FILE_REFERENCE_TYPES, MULTI_OPTION_TYPES, NUMERIC_VALUE_TYPES } from '@objectstack/spec/data';
 // [#5659] The Filter Protocol's boolean identity reduction — `$and: []` is TRUE,
 // `$or: []` is FALSE, `{}` is a TRUE disjunct, `$not: {}` is FALSE. One
@@ -8569,6 +8569,12 @@ export class SqlDriver implements IDataDriver {
     // See {@link presentReadColumns}.
     const presentedOutput = new Map<string, ReadPresentationKind>();
 
+    // [#15546] Result columns whose NULL answer folds to the identity the
+    // platform declares for that aggregate over NOTHING (`emptyGroupValueFor`,
+    // spec `data/aggregation-policy.ts`), keyed like `presentedOutput` by the
+    // column name the caller will read. See {@link foldEmptyAggregateAnswers}.
+    const foldedOutput = new Map<string, number>();
+
     if (query.groupBy) {
       // groupBy items may be plain strings ('region') or structured objects
       // ({ field: 'closed_at', dateGranularity: 'quarter' }). For structured
@@ -8698,6 +8704,12 @@ export class SqlDriver implements IDataDriver {
           } else {
             builder.select(this.knex.raw(`${rawFunc} as ${this.aliasIdentifierSql(agg.alias)}`, [fieldExpr]));
           }
+          // [#15546] What this aggregate answers over NOTHING, read from the
+          // policy rather than restated: `sum` (and the two counts, which never
+          // arrive as NULL) fold to `0`; `avg`/`min`/`max` have no identity and
+          // their NULL passes through. See {@link foldEmptyAggregateAnswers}.
+          const identity = emptyGroupValueFor(funcName);
+          if (identity !== undefined) foldedOutput.set(agg.alias, identity);
           // `min`/`max` are the only supported functions that hand back a value
           // OF the column rather than a count/total derived from it, so they are
           // the only ones whose result still needs the column's presentation.
@@ -8789,7 +8801,60 @@ export class SqlDriver implements IDataDriver {
       // {@link SqlDriver.aggregateBackendFault}.
       throw this.aggregateBackendFault(object, query, error);
     }
-    return this.presentReadColumns(rows, presentedOutput);
+    return this.presentReadColumns(this.foldEmptyAggregateAnswers(rows, foldedOutput), presentedOutput);
+  }
+
+  /**
+   * [#15546] Fold the NULL a SQL aggregate answers over an all-NULL aggregand
+   * to the identity the platform declares for that aggregate over NOTHING.
+   *
+   * SQL `SUM` skips NULLs, and once it has skipped every row of a group it
+   * answers NULL — on every dialect this driver targets. Measured 2026-09-07
+   * on better-sqlite3, live PostgreSQL 16.13 and live MySQL 8.0.46: `sum` over
+   * a group of three rows whose column is NULL in each of them is `null` on
+   * all three, for `number` and `currency` columns alike. The engine's
+   * in-memory aggregate tier (`objectql`'s `in-memory-aggregation.ts`) answers
+   * `0` for the same rows, as do `driver-memory` and `driver-mongodb`'s
+   * lowering, and `emptyGroupValueFor` (spec `data/aggregation-policy.ts`)
+   * rules that summing nothing is `0` — a measured fact, not missing data.
+   * Which face answered was decided by a driver capability bit the caller
+   * never sees (`engine.ts`'s `typeof drv.aggregate === 'function'` fork), so
+   * one grouped list view rendered a blank total on one deployment and `0` on
+   * another. Maintainer ruling 2026-09-07 on #15546 (option A): three rows
+   * whose aggregand is absent and zero rows are the SAME case for `sum` — the
+   * addend set is empty either way — and this face is the one that moves.
+   *
+   * The identity is READ from the policy rather than restated here, so the
+   * other half of the same rule holds by construction: an aggregate whose
+   * `emptyGroupValueFor` is `undefined` (`avg`/`min`/`max`) has no answer over
+   * nothing, is never registered, and its NULL reaches the caller untouched.
+   * `count`/`count_distinct` register too but never arrive as NULL — `COUNT`
+   * answers `0` on its own — so the entry is inert for them, deliberately
+   * rather than special-cased away.
+   *
+   * Presentation, not compilation. The statement is unchanged — no `COALESCE`
+   * — so the emitted-SQL pins and the per-dialect result-type parsing above
+   * are untouched, and the answer is the JS number `0` on every dialect, the
+   * same value the in-memory tier produces. Only `null` folds: an `undefined`
+   * would mean the column was never projected, a different defect that must
+   * stay visible. Rows are mutated in place, as {@link presentReadColumns}
+   * does. The unaliased branch of {@link SqlDriver.aggregate} is not tracked,
+   * for the reason `presentedOutput` gives: `alias` is required by
+   * `AggregationNodeSchema`, and that branch lands under a dialect-dependent
+   * column name.
+   *
+   * Pinned on every enrolled face by the `sum(amount)` cases of
+   * `AGGREGATION_CASES` (spec `data/aggregation-conformance.ts`).
+   */
+  protected foldEmptyAggregateAnswers(rows: any, identities: Map<string, number>): any {
+    if (identities.size === 0 || !Array.isArray(rows)) return rows;
+    for (const row of rows) {
+      if (!row || typeof row !== 'object') continue;
+      for (const [column, identity] of identities) {
+        if (row[column] === null) row[column] = identity;
+      }
+    }
+    return rows;
   }
 
   /**

packages/drivers/driver-sqlite-wasm/src/sqlite-wasm-aggregation-conformance.test.ts

@@ -48,7 +48,10 @@ const actualFor = (c: AggregationCase, rows: Array<Record<string, unknown>>) =>
   // this axis exists to catch: it is green on a face that ignores the alias.
   const groupKey = c.groupByAlias ?? c.groupBy;
   return rows
-    .map((r) => ({ group: groupKey ? String(r[groupKey]) : null, value: Number(r.n) }))
+    // [#15546] A NULL answer stays `null` — `Number(null)` is `0`, the ruled
+    // answer for the all-null `sum` cell, so coercing would let a face that
+    // hands SQL's NULL through pass as if it had folded.
+    .map((r) => ({ group: groupKey ? String(r[groupKey]) : null, value: r.n === null ? null : Number(r.n) }))
     .sort((x, y) => String(x.group).localeCompare(String(y.group)));
 };
 
@@ -66,6 +69,10 @@ describe('[#6409] driver-sqlite-wasm — aggregate vocabulary conformance', () =
           // column nullable, which is what the null-bearing rows need.
           stage: { type: 'string' },
           score: { type: 'number' },
+          // [#15546] Nullable, like `stage` — see `AggregationRow.amount`: the
+          // `east` group is NULL in every row, the cell the ruled `sum` → `0`
+          // answer is pinned on.
+          amount: { type: 'number' },
           // [#11152] Declared `type: 'boolean'` on purpose — see
           // `AggregationRow.flag`: the ruled boolean cases answer NUMBERS
           // (min=0/max=1) over the 0/1 INTEGER storage.

packages/drivers/driver-turso/src/remote-transport.ts

@@ -34,7 +34,7 @@ import { resolveFilterSubtreeProvenance } from '@objectstack/spec/data';
 // The DECLARED aggregate vocabulary (#5907) — read from the spec so this
 // transport's "the protocol has no such function" refusal cannot drift from what
 // `AggregationNodeSchema.function` admits, nor from the local driver's twin.
-import { AggregationFunction } from '@objectstack/spec/data';
+import { AggregationFunction, emptyGroupValueFor } from '@objectstack/spec/data';
 import type { DriverQuery } from '@objectstack/spec/contracts';
 // [#8413] What a `unique: true` FIELD becomes, from the one place that decides
 // it. `uniqueIndexesFromFields`' own contract is that it is "the ONLY place
@@ -1369,6 +1369,10 @@ export class RemoteTransport {
     this.assertSafeIdentifier(object);
 
     const selectParts: string[] = [];
+    // [#15546] Result columns whose NULL answer folds to the identity the
+    // platform declares for that aggregate over NOTHING — the twin of
+    // `SqlDriver.aggregate`'s `foldedOutput`. See {@link foldEmptyAggregateAnswers}.
+    const foldedOutput = new Map<string, number>();
 
     // [#6212] `groupBy` is `GroupByNode[]` — a UNION of a bare field name and a
     // structured `{ field, dateGranularity?, alias? }` entry — so reading it as
@@ -1501,6 +1505,13 @@ export class RemoteTransport {
       const alias = agg.alias || `${func}_${field === '*' ? 'all' : field}`;
       const argSql = lowering.distinct ? `distinct ${fieldSql}` : fieldSql;
       selectParts.push(`${lowering.sql}(${argSql}) AS ${this.aliasIdentifierSql(alias)}`);
+      // [#15546] What this aggregate answers over NOTHING, read from the policy
+      // rather than restated: `sum` (and the two counts, which never arrive as
+      // NULL) fold to `0`; `avg`/`min`/`max` have no identity and their NULL
+      // passes through. Keyed by the OUTPUT column — every aggregation here
+      // has one, defaulted or caller-supplied.
+      const identity = emptyGroupValueFor(func);
+      if (identity !== undefined) foldedOutput.set(alias, identity);
     }
 
     if (selectParts.length === 0) selectParts.push('*');
@@ -1524,7 +1535,7 @@ export class RemoteTransport {
 
     try {
       const result = await this.client!.execute({ sql, args });
-      return this.mapRows(result);
+      return this.foldEmptyAggregateAnswers(this.mapRows(result), foldedOutput);
     } catch (error: any) {
       if (
         error.message &&
@@ -1537,6 +1548,38 @@ export class RemoteTransport {
     }
   }
 
+  /**
+   * [#15546] Fold the NULL SQL answers for an aggregate over an all-NULL
+   * aggregand to the identity the platform declares for that aggregate over
+   * NOTHING — the twin of `SqlDriver.foldEmptyAggregateAnswers`, and the reason
+   * it is here: `TursoDriver` picks this compiler or the local one from `url`,
+   * so without it the SAME driver answered `sum` over a group whose column is
+   * NULL in every row as `0` locally and `null` remotely — the #5907/#6203
+   * shape, one query, two answers, decided by a connection string. Measured
+   * on the enrolled remote face (libsql IS SQLite) before this fold: `null`.
+   *
+   * `emptyGroupValueFor` (spec `data/aggregation-policy.ts`) is READ rather
+   * than restated, so `avg`/`min`/`max` — no identity over nothing — are never
+   * registered and their NULL reaches the caller untouched; `count` and
+   * `count_distinct` register but never arrive as NULL. Presentation, not
+   * compilation: the statement is unchanged. Only `null` folds — an
+   * `undefined` would mean the column was never projected, a different defect
+   * that must stay visible. Rows are mutated in place, as `mapRows` builds
+   * them. Pinned by the `sum(amount)` cases of `AGGREGATION_CASES`.
+   */
+  private foldEmptyAggregateAnswers(
+    rows: Record<string, unknown>[],
+    identities: Map<string, number>,
+  ): Record<string, unknown>[] {
+    if (identities.size === 0) return rows;
+    for (const row of rows) {
+      for (const [column, identity] of identities) {
+        if (row[column] === null) row[column] = identity;
+      }
+    }
+    return rows;
+  }
+
   async create(object: string, data: Record<string, unknown>): Promise<Record<string, unknown>> {
     await this.ensureConnected();
 

packages/drivers/driver-turso/src/turso-remote-aggregation-conformance.test.ts

@@ -73,6 +73,10 @@ const CONFORMANCE_OBJECT = {
     // Nullable, and it must stay that way — see `AggregationRow.stage`.
     stage: { type: 'string' },
     score: { type: 'number' },
+    // [#15546] Nullable, like `stage` — see `AggregationRow.amount`: the `east`
+    // group is NULL in every row, the cell the ruled `sum` → `0` answer is
+    // pinned on.
+    amount: { type: 'number' },
     // [#11152] Declared `type: 'boolean'` on purpose — see `AggregationRow.flag`.
     // SQLite stores it 0/1 INTEGER, and the ruled boolean cases (min=0/max=1,
     // sum=3, avg=0.5) are answered in exactly that numeric domain.
@@ -97,8 +101,12 @@ const actualFor = (c: AggregationCase, rows: Array<Record<string, unknown>>) =>
   // `groupByAlias ?? groupBy`. Reading `c.groupBy` unconditionally is the bug
   // this axis exists to catch: it is green on a face that ignores the alias.
   const groupKey = c.groupByAlias ?? c.groupBy;
+  // [#15546] A NULL answer is kept as `null`, never coerced: `Number(null)` is
+  // `0`, the ruled answer for the all-null `sum` cell, so an unconditional
+  // `Number(r.n)` reads a face that hands SQL's NULL through as if it had
+  // folded — the harness holding the observable instead of the face.
   return rows
-    .map((r) => ({ group: groupKey ? String(r[groupKey]) : null, value: Number(r.n) }))
+    .map((r) => ({ group: groupKey ? String(r[groupKey]) : null, value: r.n === null ? null : Number(r.n) }))
     .sort((x, y) => String(x.group).localeCompare(String(y.group)));
 };