diff --git a/packages/capability-matrix/capabilities/database.yaml b/packages/capability-matrix/capabilities/database.yaml
index 52d8519..b1484e8 100644
--- a/packages/capability-matrix/capabilities/database.yaml
+++ b/packages/capability-matrix/capabilities/database.yaml
@@ -14,6 +14,14 @@ groups:
   - id: configuration
     title: Client Configuration
 features:
+  - id: database.mutate.bulk_rows_with_differing_fields
+    name: Bulk Write Rows with Differing Fields
+    description: Insert or upsert multiple rows with different field sets in one request, without requiring callers to fill every omitted field explicitly.
+    group: mutate
+  - id: database.mutate.count
+    name: Count Mutated Rows
+    description: Request the number of rows affected by an insert, update, upsert, or delete operation.
+    group: mutate
   - id: database.mutate.delete
     name: Delete Rows
     description: Delete rows from a table or view that match a filter.
@@ -22,6 +30,10 @@ features:
     name: Insert Rows
     description: Insert one or more rows into a table or view.
     group: mutate
+  - id: database.mutate.missing_defaults
+    name: Use Defaults for Missing Fields
+    description: Use database column defaults instead of null for fields omitted from bulk insert or upsert rows.
+    group: mutate
   - id: database.mutate.select_after_mutation
     name: Select After Mutation
     description: Chain a column selection onto an insert, update, upsert, or delete to return the affected rows in the response.
@@ -241,4 +253,4 @@ features:
   - id: database.configuration.request_timeout
     name: Request Timeout
     description: Set a global request timeout in milliseconds at construction time; in-flight requests are cancelled once the deadline is reached.
-    group: configuration
\ No newline at end of file
+    group: configuration
diff --git a/packages/capability-matrix/specs/database/mutate/bulk_rows_with_differing_fields.md b/packages/capability-matrix/specs/database/mutate/bulk_rows_with_differing_fields.md
new file mode 100644
index 0000000..d067c3d
--- /dev/null
+++ b/packages/capability-matrix/specs/database/mutate/bulk_rows_with_differing_fields.md
@@ -0,0 +1,28 @@
+# Bulk Write Rows with Differing Fields
+
+Insert or upsert multiple rows with different field sets in one request.
+
+## API
+
+Spec: [PostgREST Documentation: Specifying Columns](https://docs.postgrest.org/en/latest/references/api/tables_views.html#specifying-columns)
+
+- `POST /{relation}?columns={union-of-fields}`
+
+## Behavior
+
+The SDK accepts a collection whose rows do not all contain the same fields and sends it as one bulk insert or upsert. It identifies the union of fields across the non-empty collection and supplies that set through PostgREST's `columns` query parameter.
+
+The SDK must not require callers to add placeholder values for omitted fields. Their values follow the missing-field behavior selected for the request.
+
+An empty collection writes nothing and must not produce an empty `columns` parameter.
+
+## Errors
+
+- `PGRST204` when a field named by `columns` does not exist
+- Database constraint errors still apply to every row in the bulk operation
+
+## Related
+
+- [Insert Rows](insert.md)
+- [Upsert Rows](upsert.md)
+- [Use Defaults for Missing Fields](missing_defaults.md)
diff --git a/packages/capability-matrix/specs/database/mutate/count.md b/packages/capability-matrix/specs/database/mutate/count.md
new file mode 100644
index 0000000..26b89cf
--- /dev/null
+++ b/packages/capability-matrix/specs/database/mutate/count.md
@@ -0,0 +1,23 @@
+# Count Mutated Rows
+
+Request the number of rows affected by an insert, update, upsert, or delete operation.
+
+## API
+
+Spec: [PostgREST Documentation: Counting](https://docs.postgrest.org/en/latest/references/api/pagination_count.html#counting)
+
+- `POST`, `PATCH`, or `DELETE` with `Prefer: count=exact|planned|estimated`
+
+## Behavior
+
+The caller chooses a supported count strategy when starting a mutation. The response exposes the resulting affected-row count separately from any returned row representation.
+
+Counting is optional. Omitting it avoids requesting a total, and selecting it must not implicitly request the mutated rows themselves.
+
+The count preference is independent of other `Prefer` entries, including `return`, `resolution`, and `missing`. An SDK must preserve those entries when adding the count preference.
+
+## Related
+
+- [Insert Rows](insert.md)
+- [Upsert Rows](upsert.md)
+- `database.mutate.select_after_mutation`
diff --git a/packages/capability-matrix/specs/database/mutate/insert.md b/packages/capability-matrix/specs/database/mutate/insert.md
index afe237b..67c99bc 100644
--- a/packages/capability-matrix/specs/database/mutate/insert.md
+++ b/packages/capability-matrix/specs/database/mutate/insert.md
@@ -48,3 +48,6 @@ whole header.
 ## Related
 
 - [Upsert Rows](upsert.md) — insert, but resolve a conflict instead of failing
+- [Bulk Write Rows with Differing Fields](bulk_rows_with_differing_fields.md)
+- [Use Defaults for Missing Fields](missing_defaults.md)
+- [Count Mutated Rows](count.md)
diff --git a/packages/capability-matrix/specs/database/mutate/missing_defaults.md b/packages/capability-matrix/specs/database/mutate/missing_defaults.md
new file mode 100644
index 0000000..cb9b1fc
--- /dev/null
+++ b/packages/capability-matrix/specs/database/mutate/missing_defaults.md
@@ -0,0 +1,27 @@
+# Use Defaults for Missing Fields
+
+Use database column defaults instead of null for fields omitted from bulk insert or upsert rows.
+
+## API
+
+Spec: [PostgREST Documentation: Missing](https://docs.postgrest.org/en/latest/references/api/preferences.html#missing)
+
+- `POST /{relation}?columns={union-of-fields}` with `Prefer: missing=default`
+
+## Behavior
+
+When rows in a bulk insert or upsert omit different fields, the caller can choose whether each omitted value becomes SQL `NULL` or uses the column's database `DEFAULT`.
+
+Using database defaults sends `missing=default`. The alternative omits that preference or sends `missing=null`. The choice only affects omitted fields. An explicitly supplied null remains null.
+
+The missing preference is independent of other `Prefer` entries, including `return`, `resolution`, and `count`. An SDK must preserve those entries when changing the missing-field behavior.
+
+## Prerequisites
+
+The request must supply a `columns` parameter containing the union of fields across the rows. Without it, a bulk payload must carry an identical key set on every row (see [Insert Rows](insert.md)), and a field omitted from every row is left out of the statement entirely, so the database applies its default regardless of this preference.
+
+## Related
+
+- [Bulk Write Rows with Differing Fields](bulk_rows_with_differing_fields.md)
+- [Insert Rows](insert.md)
+- [Upsert Rows](upsert.md)
diff --git a/packages/capability-matrix/specs/database/mutate/upsert.md b/packages/capability-matrix/specs/database/mutate/upsert.md
index 18e0d3c..2c072c6 100644
--- a/packages/capability-matrix/specs/database/mutate/upsert.md
+++ b/packages/capability-matrix/specs/database/mutate/upsert.md
@@ -45,3 +45,6 @@ the whole header drops `resolution=` and silently turns the upsert into an inser
 ## Related
 
 - [Insert Rows](insert.md) — the same write without conflict resolution
+- [Bulk Write Rows with Differing Fields](bulk_rows_with_differing_fields.md)
+- [Use Defaults for Missing Fields](missing_defaults.md)
+- [Count Mutated Rows](count.md)