Fixed #35444 -- Added generic support for Aggregate.order_by.

This moves the behaviors of `order_by` used in Postgres aggregates into
the `Aggregate` class. This allows for creating aggregate functions that
support this behavior across all database engines. This is shown by
moving the `StringAgg` class into the shared `aggregates` module and
adding support for all databases. The Postgres `StringAgg` class is now
a thin wrapper on the new shared `StringAgg` class.

Thank you Simon Charette for the review.

19 files changed, 658 insertions, 290 deletions

diff --git a/django/contrib/gis/db/models/aggregates.py b/django/contrib/gis/db/models/aggregates.py
index abff1a5206..264bef7021 100644
--- a/django/contrib/gis/db/models/aggregates.py
+++ b/django/contrib/gis/db/models/aggregates.py
@@ -33,15 +33,14 @@ class GeoAggregate(Aggregate):
         if not self.is_extent:
             tolerance = self.extra.get("tolerance") or getattr(self, "tolerance", 0.05)
             clone = self.copy()
-            source_expressions = self.get_source_expressions()
-            source_expressions.pop()  # Don't wrap filters with SDOAGGRTYPE().
+            *source_exprs, filter_expr, order_by_expr = self.get_source_expressions()
             spatial_type_expr = Func(
-                *source_expressions,
+                *source_exprs,
                 Value(tolerance),
                 function="SDOAGGRTYPE",
                 output_field=self.output_field,
             )
-            source_expressions = [spatial_type_expr, self.filter]
+            source_expressions = [spatial_type_expr, filter_expr, order_by_expr]
             clone.set_source_expressions(source_expressions)
             return clone.as_sql(compiler, connection, **extra_context)
         return self.as_sql(compiler, connection, **extra_context)
diff --git a/django/contrib/postgres/aggregates/general.py b/django/contrib/postgres/aggregates/general.py
index 48968b51b8..153b0242e3 100644
--- a/django/contrib/postgres/aggregates/general.py
+++ b/django/contrib/postgres/aggregates/general.py
@@ -1,7 +1,12 @@
+import warnings
+
 from django.contrib.postgres.fields import ArrayField
-from django.db.models import Aggregate, BooleanField, JSONField, TextField, Value
+from django.db.models import Aggregate, BooleanField, JSONField
+from django.db.models import StringAgg as _StringAgg
+from django.db.models import Value
+from django.utils.deprecation import RemovedInDjango70Warning
 
-from .mixins import OrderableAggMixin
+from .mixins import _DeprecatedOrdering
 
 __all__ = [
     "ArrayAgg",
@@ -11,14 +16,16 @@ __all__ = [
     "BoolAnd",
     "BoolOr",
     "JSONBAgg",
-    "StringAgg",
+    "StringAgg",  # RemovedInDjango70Warning.
 ]
 
 
-class ArrayAgg(OrderableAggMixin, Aggregate):
+# RemovedInDjango61Warning: When the deprecation ends, replace with:
+# class ArrayAgg(Aggregate):
+class ArrayAgg(_DeprecatedOrdering, Aggregate):
     function = "ARRAY_AGG"
-    template = "%(function)s(%(distinct)s%(expressions)s %(order_by)s)"
     allow_distinct = True
+    allow_order_by = True
 
     @property
     def output_field(self):
@@ -47,19 +54,37 @@ class BoolOr(Aggregate):
     output_field = BooleanField()
 
 
-class JSONBAgg(OrderableAggMixin, Aggregate):
+# RemovedInDjango61Warning: When the deprecation ends, replace with:
+# class JSONBAgg(Aggregate):
+class JSONBAgg(_DeprecatedOrdering, Aggregate):
     function = "JSONB_AGG"
-    template = "%(function)s(%(distinct)s%(expressions)s %(order_by)s)"
     allow_distinct = True
+    allow_order_by = True
     output_field = JSONField()
 
 
-class StringAgg(OrderableAggMixin, Aggregate):
-    function = "STRING_AGG"
-    template = "%(function)s(%(distinct)s%(expressions)s %(order_by)s)"
-    allow_distinct = True
-    output_field = TextField()
+# RemovedInDjango61Warning: When the deprecation ends, replace with:
+# class StringAgg(_StringAgg):
+# RemovedInDjango70Warning: When the deprecation ends, remove completely.
+class StringAgg(_DeprecatedOrdering, _StringAgg):
 
     def __init__(self, expression, delimiter, **extra):
-        delimiter_expr = Value(str(delimiter))
-        super().__init__(expression, delimiter_expr, **extra)
+        if isinstance(delimiter, str):
+            warnings.warn(
+                "delimiter: str will be resolved as a field reference instead "
+                "of a string literal on Django 7.0. Pass "
+                f"`delimiter=Value({delimiter!r})` to preserve the previous behaviour.",
+                category=RemovedInDjango70Warning,
+                stacklevel=2,
+            )
+
+            delimiter = Value(delimiter)
+
+        warnings.warn(
+            "The PostgreSQL specific StringAgg function is deprecated. Use "
+            "django.db.models.aggregate.StringAgg instead.",
+            category=RemovedInDjango70Warning,
+            stacklevel=2,
+        )
+
+        super().__init__(expression, delimiter, **extra)
diff --git a/django/contrib/postgres/aggregates/mixins.py b/django/contrib/postgres/aggregates/mixins.py
index 6af43a7fea..bc416350ad 100644
--- a/django/contrib/postgres/aggregates/mixins.py
+++ b/django/contrib/postgres/aggregates/mixins.py
@@ -1,15 +1,11 @@
 import warnings
 
-from django.core.exceptions import FullResultSet
-from django.db.models.expressions import OrderByList
 from django.utils.deprecation import RemovedInDjango61Warning
 
 
-class OrderableAggMixin:
-    # RemovedInDjango61Warning: When the deprecation ends, replace with:
-    # def __init__(self, *expressions, order_by=(), **extra):
+# RemovedInDjango61Warning.
+class _DeprecatedOrdering:
     def __init__(self, *expressions, ordering=(), order_by=(), **extra):
-        # RemovedInDjango61Warning.
         if ordering:
             warnings.warn(
                 "The ordering argument is deprecated. Use order_by instead.",
@@ -19,44 +15,14 @@ class OrderableAggMixin:
             if order_by:
                 raise TypeError("Cannot specify both order_by and ordering.")
             order_by = ordering
-        if not order_by:
-            self.order_by = None
-        elif isinstance(order_by, (list, tuple)):
-            self.order_by = OrderByList(*order_by)
-        else:
-            self.order_by = OrderByList(order_by)
-        super().__init__(*expressions, **extra)
 
-    def resolve_expression(self, *args, **kwargs):
-        if self.order_by is not None:
-            self.order_by = self.order_by.resolve_expression(*args, **kwargs)
-        return super().resolve_expression(*args, **kwargs)
+        super().__init__(*expressions, order_by=order_by, **extra)
 
-    def get_source_expressions(self):
-        return super().get_source_expressions() + [self.order_by]
 
-    def set_source_expressions(self, exprs):
-        *exprs, self.order_by = exprs
-        return super().set_source_expressions(exprs)
+# RemovedInDjango61Warning: When the deprecation ends, replace with:
+# class OrderableAggMixin:
+class OrderableAggMixin(_DeprecatedOrdering):
+    allow_order_by = True
 
-    def as_sql(self, compiler, connection):
-        *source_exprs, filtering_expr, order_by_expr = self.get_source_expressions()
-
-        order_by_sql = ""
-        order_by_params = []
-        if order_by_expr is not None:
-            order_by_sql, order_by_params = compiler.compile(order_by_expr)
-
-        filter_params = []
-        if filtering_expr is not None:
-            try:
-                _, filter_params = compiler.compile(filtering_expr)
-            except FullResultSet:
-                pass
-
-        source_params = []
-        for source_expr in source_exprs:
-            source_params += compiler.compile(source_expr)[1]
-
-        sql, _ = super().as_sql(compiler, connection, order_by=order_by_sql)
-        return sql, (*source_params, *order_by_params, *filter_params)
+    def __init_subclass__(cls, /, *args, **kwargs):
+        super().__init_subclass__(*args, **kwargs)
diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index 0f8e6f41a6..95230bb06b 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -257,6 +257,15 @@ class BaseDatabaseFeatures:
     # expressions?
     supports_aggregate_filter_clause = False
 
+    # Does the database support ORDER BY in aggregate expressions?
+    supports_aggregate_order_by_clause = False
+
+    # Does the database backend support DISTINCT when using multiple arguments in an
+    # aggregate expression? For example, Sqlite treats the "delimiter" argument of
+    # STRING_AGG/GROUP_CONCAT as an extra argument and does not allow using a custom
+    # delimiter along with DISTINCT.
+    supports_aggregate_distinct_multiple_argument = True
+
     # Does the backend support indexing a TextField?
     supports_index_on_text_field = True
 
diff --git a/django/db/backends/mysql/features.py b/django/db/backends/mysql/features.py
index 6e1b64c502..5570ede203 100644
--- a/django/db/backends/mysql/features.py
+++ b/django/db/backends/mysql/features.py
@@ -19,6 +19,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     requires_explicit_null_ordering_when_grouping = True
     atomic_transactions = False
     can_clone_databases = True
+    supports_aggregate_order_by_clause = True
     supports_comments = True
     supports_comments_inline = True
     supports_temporal_subtraction = True
diff --git a/django/db/backends/oracle/features.py b/django/db/backends/oracle/features.py
index 559a36bfed..c9bcc84b32 100644
--- a/django/db/backends/oracle/features.py
+++ b/django/db/backends/oracle/features.py
@@ -45,6 +45,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     # does by uppercasing all identifiers.
     ignores_table_name_case = True
     supports_index_on_text_field = False
+    supports_aggregate_order_by_clause = True
     create_test_procedure_without_params_sql = """
         CREATE PROCEDURE "TEST_PROCEDURE" AS
             V_I INTEGER;
diff --git a/django/db/backends/postgresql/features.py b/django/db/backends/postgresql/features.py
index 16653a0519..d410e56e69 100644
--- a/django/db/backends/postgresql/features.py
+++ b/django/db/backends/postgresql/features.py
@@ -64,6 +64,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_frame_exclusion = True
     only_supports_unbounded_with_preceding_and_following = True
     supports_aggregate_filter_clause = True
+    supports_aggregate_order_by_clause = True
     supported_explain_formats = {"JSON", "TEXT", "XML", "YAML"}
     supports_deferrable_unique_constraints = True
     has_json_operators = True
diff --git a/django/db/backends/sqlite3/features.py b/django/db/backends/sqlite3/features.py
index 60893561df..88ec6767a0 100644
--- a/django/db/backends/sqlite3/features.py
+++ b/django/db/backends/sqlite3/features.py
@@ -34,6 +34,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_frame_range_fixed_distance = True
     supports_frame_exclusion = True
     supports_aggregate_filter_clause = True
+    supports_aggregate_order_by_clause = Database.sqlite_version_info >= (3, 44, 0)
+    supports_aggregate_distinct_multiple_argument = False
     order_by_nulls_first = True
     supports_json_field_contains = False
     supports_update_conflicts = True
diff --git a/django/db/models/aggregates.py b/django/db/models/aggregates.py
index ea16cc440c..a791593508 100644
--- a/django/db/models/aggregates.py
+++ b/django/db/models/aggregates.py
@@ -3,8 +3,17 @@ Classes to represent the definitions of aggregate functions.
 """
 
 from django.core.exceptions import FieldError, FullResultSet
-from django.db.models.expressions import Case, ColPairs, Func, Star, Value, When
-from django.db.models.fields import IntegerField
+from django.db import NotSupportedError
+from django.db.models.expressions import (
+    Case,
+    ColPairs,
+    Func,
+    OrderByList,
+    Star,
+    Value,
+    When,
+)
+from django.db.models.fields import IntegerField, TextField
 from django.db.models.functions import Coalesce
 from django.db.models.functions.mixins import (
     FixDurationInputMixin,
@@ -18,42 +27,91 @@ __all__ = [
     "Max",
     "Min",
     "StdDev",
+    "StringAgg",
     "Sum",
     "Variance",
 ]
 
 
+class AggregateFilter(Func):
+    arity = 1
+    template = " FILTER (WHERE %(expressions)s)"
+
+    def as_sql(self, compiler, connection, **extra_context):
+        if not connection.features.supports_aggregate_filter_clause:
+            raise NotSupportedError(
+                "Aggregate filter clauses are not supported on this database backend."
+            )
+        try:
+            return super().as_sql(compiler, connection, **extra_context)
+        except FullResultSet:
+            return "", ()
+
+    @property
+    def condition(self):
+        return self.source_expressions[0]
+
+    def __str__(self):
+        return self.arg_joiner.join(str(arg) for arg in self.source_expressions)
+
+
+class AggregateOrderBy(OrderByList):
+    template = " ORDER BY %(expressions)s"
+
+    def as_sql(self, compiler, connection, **extra_context):
+        if not connection.features.supports_aggregate_order_by_clause:
+            raise NotSupportedError(
+                "This database backend does not support specifying an order on "
+                "aggregates."
+            )
+
+        return super().as_sql(compiler, connection, **extra_context)
+
+
 class Aggregate(Func):
-    template = "%(function)s(%(distinct)s%(expressions)s)"
+    template = "%(function)s(%(distinct)s%(expressions)s%(order_by)s)%(filter)s"
     contains_aggregate = True
     name = None
-    filter_template = "%s FILTER (WHERE %%(filter)s)"
     window_compatible = True
     allow_distinct = False
+    allow_order_by = False
     empty_result_set_value = None
 
     def __init__(
-        self, *expressions, distinct=False, filter=None, default=None, **extra
+        self,
+        *expressions,
+        distinct=False,
+        filter=None,
+        default=None,
+        order_by=None,
+        **extra,
     ):
         if distinct and not self.allow_distinct:
             raise TypeError("%s does not allow distinct." % self.__class__.__name__)
+        if order_by and not self.allow_order_by:
+            raise TypeError("%s does not allow order_by." % self.__class__.__name__)
         if default is not None and self.empty_result_set_value is not None:
             raise TypeError(f"{self.__class__.__name__} does not allow default.")
+
         self.distinct = distinct
-        self.filter = filter
+        self.filter = filter and AggregateFilter(filter)
         self.default = default
+        self.order_by = AggregateOrderBy.from_param(
+            f"{self.__class__.__name__}.order_by", order_by
+        )
         super().__init__(*expressions, **extra)
 
     def get_source_fields(self):
-        # Don't return the filter expression since it's not a source field.
+        # Don't consider filter and order by expression as they have nothing
+        # to do with the output field resolution.
         return [e._output_field_or_none for e in super().get_source_expressions()]
 
     def get_source_expressions(self):
         source_expressions = super().get_source_expressions()
-        return source_expressions + [self.filter]
+        return source_expressions + [self.filter, self.order_by]
 
     def set_source_expressions(self, exprs):
-        *exprs, self.filter = exprs
+        *exprs, self.filter, self.order_by = exprs
         return super().set_source_expressions(exprs)
 
     def resolve_expression(
@@ -66,6 +124,11 @@ class Aggregate(Func):
             if c.filter
             else None
         )
+        c.order_by = (
+            c.order_by.resolve_expression(query, allow_joins, reuse, summarize)
+            if c.order_by
+            else None
+        )
         if summarize:
             # Summarized aggregates cannot refer to summarized aggregates.
             for ref in c.get_refs():
@@ -115,35 +178,45 @@ class Aggregate(Func):
         return []
 
     def as_sql(self, compiler, connection, **extra_context):
-        extra_context["distinct"] = "DISTINCT " if self.distinct else ""
-        if self.filter:
-            if connection.features.supports_aggregate_filter_clause:
-                try:
-                    filter_sql, filter_params = self.filter.as_sql(compiler, connection)
-                except FullResultSet:
-                    pass
-                else:
-                    template = self.filter_template % extra_context.get(
-                        "template", self.template
-                    )
-                    sql, params = super().as_sql(
-                        compiler,
-                        connection,
-                        template=template,
-                        filter=filter_sql,
-                        **extra_context,
-                    )
-                    return sql, (*params, *filter_params)
-            else:
+        if (
+            self.distinct
+            and not connection.features.supports_aggregate_distinct_multiple_argument
+            and len(super().get_source_expressions()) > 1
+        ):
+            raise NotSupportedError(
+                f"{self.name} does not support distinct with multiple expressions on "
+                f"this database backend."
+            )
+
+        distinct_sql = "DISTINCT " if self.distinct else ""
+        order_by_sql = ""
+        order_by_params = []
+        filter_sql = ""
+        filter_params = []
+
+        if (order_by := self.order_by) is not None:
+            order_by_sql, order_by_params = compiler.compile(order_by)
+
+        if self.filter is not None:
+            try:
+                filter_sql, filter_params = compiler.compile(self.filter)
+            except NotSupportedError:
+                # Fallback to a CASE statement on backends that don't support
+                # the FILTER clause.
                 copy = self.copy()
                 copy.filter = None
                 source_expressions = copy.get_source_expressions()
-                condition = When(self.filter, then=source_expressions[0])
+                condition = When(self.filter.condition, then=source_expressions[0])
                 copy.set_source_expressions([Case(condition)] + source_expressions[1:])
-                return super(Aggregate, copy).as_sql(
-                    compiler, connection, **extra_context
-                )
-        return super().as_sql(compiler, connection, **extra_context)
+                return copy.as_sql(compiler, connection, **extra_context)
+
+        extra_context.update(
+            distinct=distinct_sql,
+            filter=filter_sql,
+            order_by=order_by_sql,
+        )
+        sql, params = super().as_sql(compiler, connection, **extra_context)
+        return sql, (*params, *order_by_params, *filter_params)
 
     def _get_repr_options(self):
         options = super()._get_repr_options()
@@ -151,6 +224,8 @@ class Aggregate(Func):
             options["distinct"] = self.distinct
         if self.filter:
             options["filter"] = self.filter
+        if self.order_by:
+            options["order_by"] = self.order_by
         return options
 
 
@@ -179,17 +254,17 @@ class Count(Aggregate):
 
     def resolve_expression(self, *args, **kwargs):
         result = super().resolve_expression(*args, **kwargs)
-        expr = result.source_expressions[0]
+        source_expressions = result.get_source_expressions()
 
         # In case of composite primary keys, count the first column.
-        if isinstance(expr, ColPairs):
+        if isinstance(expr := source_expressions[0], ColPairs):
             if self.distinct:
                 raise ValueError(
                     "COUNT(DISTINCT) doesn't support composite primary keys"
                 )
 
-            cols = expr.get_cols()
-            return Count(cols[0], filter=result.filter)
+            source_expressions[0] = expr.get_cols()[0]
+            result.set_source_expressions(source_expressions)
 
         return result
 
@@ -218,6 +293,88 @@ class StdDev(NumericOutputFieldMixin, Aggregate):
         return {**super()._get_repr_options(), "sample": self.function == "STDDEV_SAMP"}
 
 
+class StringAggDelimiter(Func):
+    arity = 1
+    template = "%(expressions)s"
+
+    def __init__(self, value):
+        self.value = value
+        super().__init__(value)
+
+    def as_mysql(self, compiler, connection, **extra_context):
+        template = " SEPARATOR %(expressions)s"
+
+        return self.as_sql(
+            compiler,
+            connection,
+            template=template,
+            **extra_context,
+        )
+
+
+class StringAgg(Aggregate):
+    template = "%(function)s(%(distinct)s%(expressions)s%(order_by)s)%(filter)s"
+    function = "STRING_AGG"
+    name = "StringAgg"
+    allow_distinct = True
+    allow_order_by = True
+    output_field = TextField()
+
+    def __init__(self, expression, delimiter, **extra):
+        self.delimiter = StringAggDelimiter(delimiter)
+        super().__init__(expression, self.delimiter, **extra)
+
+    def as_oracle(self, compiler, connection, **extra_context):
+        if self.order_by:
+            template = (
+                "%(function)s(%(distinct)s%(expressions)s) WITHIN GROUP (%(order_by)s)"
+                "%(filter)s"
+            )
+        else:
+            template = "%(function)s(%(distinct)s%(expressions)s)%(filter)s"
+
+        return self.as_sql(
+            compiler,
+            connection,
+            function="LISTAGG",
+            template=template,
+            **extra_context,
+        )
+
+    def as_mysql(self, compiler, connection, **extra_context):
+        extra_context["function"] = "GROUP_CONCAT"
+
+        template = "%(function)s(%(distinct)s%(expressions)s%(order_by)s%(delimiter)s)"
+        extra_context["template"] = template
+
+        c = self.copy()
+        # The creation of the delimiter SQL and the ordering of the parameters must be
+        # handled explicitly, as MySQL puts the delimiter at the end of the aggregate
+        # using the `SEPARATOR` declaration (rather than treating as an expression like
+        # other database backends).
+        delimiter_params = []
+        if c.delimiter:
+            delimiter_sql, delimiter_params = compiler.compile(c.delimiter)
+            # Drop the delimiter from the source expressions.
+            c.source_expressions = c.source_expressions[:-1]
+            extra_context["delimiter"] = delimiter_sql
+
+        sql, params = c.as_sql(compiler, connection, **extra_context)
+
+        return sql, (*params, *delimiter_params)
+
+    def as_sqlite(self, compiler, connection, **extra_context):
+        if connection.get_database_version() < (3, 44):
+            return self.as_sql(
+                compiler,
+                connection,
+                function="GROUP_CONCAT",
+                **extra_context,
+            )
+
+        return self.as_sql(compiler, connection, **extra_context)
+
+
 class Sum(FixDurationInputMixin, Aggregate):
     function = "SUM"
     name = "Sum"
diff --git a/django/db/models/expressions.py b/django/db/models/expressions.py
index ced8779637..b55a9dc74c 100644
--- a/django/db/models/expressions.py
+++ b/django/db/models/expressions.py
@@ -1481,6 +1481,21 @@ class OrderByList(ExpressionList):
         )
         super().__init__(*expressions, **extra)
 
+    @classmethod
+    def from_param(cls, context, param):
+        if param is None:
+            return None
+        if isinstance(param, (list, tuple)):
+            if not param:
+                return None
+            return cls(*param)
+        elif isinstance(param, str) or hasattr(param, "resolve_expression"):
+            return cls(param)
+        raise ValueError(
+            f"{context} must be either a string reference to a "
+            f"field, an expression, or a list or tuple of them not {param!r}."
+        )
+
 
 @deconstructible(path="django.db.models.ExpressionWrapper")
 class ExpressionWrapper(SQLiteNumericMixin, Expression):
@@ -1943,16 +1958,7 @@ class Window(SQLiteNumericMixin, Expression):
                 self.partition_by = (self.partition_by,)
             self.partition_by = ExpressionList(*self.partition_by)
 
-        if self.order_by is not None:
-            if isinstance(self.order_by, (list, tuple)):
-                self.order_by = OrderByList(*self.order_by)
-            elif isinstance(self.order_by, (BaseExpression, str)):
-                self.order_by = OrderByList(self.order_by)
-            else:
-                raise ValueError(
-                    "Window.order_by must be either a string reference to a "
-                    "field, an expression, or a list or tuple of them."
-                )
+        self.order_by = OrderByList.from_param("Window.order_by", self.order_by)
         super().__init__(output_field=output_field)
         self.source_expression = self._parse_expressions(expression)[0]
 
diff --git a/docs/internals/deprecation.txt b/docs/internals/deprecation.txt
index 0a8ccaa20a..a7695972eb 100644
--- a/docs/internals/deprecation.txt
+++ b/docs/internals/deprecation.txt
@@ -18,6 +18,8 @@ details on these changes.
 * The ``serialize`` keyword argument of
   ``BaseDatabaseCreation.create_test_db()`` will be removed.
 
+* The ``django.contrib.postgres.aggregates.StringAgg`` class will be removed.
+
 .. _deprecation-removed-in-6.1:
 
 6.1
diff --git a/docs/ref/contrib/postgres/aggregates.txt b/docs/ref/contrib/postgres/aggregates.txt
index 80c8acf80b..d590eb384f 100644
--- a/docs/ref/contrib/postgres/aggregates.txt
+++ b/docs/ref/contrib/postgres/aggregates.txt
@@ -194,6 +194,8 @@ General-purpose aggregation functions
 
 .. class:: StringAgg(expression, delimiter, distinct=False, filter=None, default=None, order_by=())
 
+    .. deprecated:: 6.0
+
     Returns the input values concatenated into a string, separated by
     the ``delimiter`` string, or ``default`` if there are no values.
 
diff --git a/docs/ref/models/expressions.txt b/docs/ref/models/expressions.txt
index 6a6356b3bb..c3c9ebba7a 100644
--- a/docs/ref/models/expressions.txt
+++ b/docs/ref/models/expressions.txt
@@ -448,7 +448,7 @@ some complex computations::
 
 The ``Aggregate`` API is as follows:
 
-.. class:: Aggregate(*expressions, output_field=None, distinct=False, filter=None, default=None, **extra)
+.. class:: Aggregate(*expressions, output_field=None, distinct=False, filter=None, default=None, order_by=None, **extra)
 
     .. attribute:: template
 
@@ -473,6 +473,15 @@ The ``Aggregate`` API is as follows:
         allows passing a ``distinct`` keyword argument. If set to ``False``
         (default), ``TypeError`` is raised if ``distinct=True`` is passed.
 
+    .. attribute:: allow_order_by
+
+        .. versionadded:: 6.0
+
+        A class attribute determining whether or not this aggregate function
+        allows passing a ``order_by`` keyword argument. If set to ``False``
+        (default), ``TypeError`` is raised if ``order_by`` is passed as a value
+        other than ``None``.
+
     .. attribute:: empty_result_set_value
 
         Defaults to ``None`` since most aggregate functions result in ``NULL``
@@ -491,6 +500,12 @@ The ``filter`` argument takes a :class:`Q object <django.db.models.Q>` that's
 used to filter the rows that are aggregated. See :ref:`conditional-aggregation`
 and :ref:`filtering-on-annotations` for example usage.
 
+The ``order_by`` argument behaves similarly to the ``field_names`` input of the
+:meth:`~.QuerySet.order_by` function, accepting a field name (with an optional
+``"-"`` prefix which indicates descending order) or an expression (or a tuple
+or list of strings and/or expressions) that specifies the ordering of the
+elements in the result.
+
 The ``default`` argument takes a value that will be passed along with the
 aggregate to :class:`~django.db.models.functions.Coalesce`. This is useful for
 specifying a value to be returned other than ``None`` when the queryset (or
@@ -499,6 +514,10 @@ grouping) contains no entries.
 The ``**extra`` kwargs are ``key=value`` pairs that can be interpolated
 into the ``template`` attribute.
 
+.. versionchanged:: 6.0
+
+    The ``order_by`` argument was added.
+
 Creating your own Aggregate Functions
 -------------------------------------
 
diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt
index 8bf83838c0..06d2086328 100644
--- a/docs/ref/models/querysets.txt
+++ b/docs/ref/models/querysets.txt
@@ -4046,6 +4046,25 @@ by the aggregate.
         However, if ``sample=True``, the return value will be the sample
         variance.
 
+``StringAgg``
+~~~~~~~~~~~~~
+
+.. versionadded:: 6.0
+
+.. class:: StringAgg(expression, delimiter, output_field=None, distinct=False, filter=None, order_by=None, default=None, **extra)
+
+    Returns the input values concatenated into a string, separated by the
+    ``delimiter`` string, or ``default`` if there are no values.
+
+    * Default alias: ``<field>__stringagg``
+    * Return type: ``string`` or ``output_field`` if supplied. If the
+      queryset or grouping is empty, ``default`` is returned.
+
+    .. attribute:: delimiter
+
+        A ``Value`` or expression representing the string that should separate
+        each of the values. For example, ``Value(",")``.
+
 Query-related tools
 ===================
 
diff --git a/docs/releases/6.0.txt b/docs/releases/6.0.txt
index 5d173c981f..edf4ce0299 100644
--- a/docs/releases/6.0.txt
+++ b/docs/releases/6.0.txt
@@ -184,6 +184,16 @@ Models
 * :doc:`Constraints </ref/models/constraints>` now implement a ``check()``
   method that is already registered with the check framework.
 
+* The new ``order_by`` argument for :class:`~django.db.models.Aggregate` allows
+  specifying the ordering of the elements in the result.
+
+* The new :attr:`.Aggregate.allow_order_by` class attribute determines whether
+  the aggregate function allows passing an ``order_by`` keyword argument.
+
+* The new :class:`~django.db.models.StringAgg` aggregate returns the input
+  values concatenated into a string, separated by the ``delimiter`` string.
+  This aggregate was previously supported only for PostgreSQL.
+
 Requests and Responses
 ~~~~~~~~~~~~~~~~~~~~~~
 
@@ -288,6 +298,9 @@ Miscellaneous
 * ``BaseDatabaseCreation.create_test_db(serialize)`` is deprecated. Use
   ``serialize_db_to_string()`` instead.
 
+* The PostgreSQL ``StringAgg`` class is deprecated in favor of the generally
+  available :class:`~django.db.models.StringAgg` class.
+
 Features removed in 6.0
 =======================
 
diff --git a/tests/aggregation/models.py b/tests/aggregation/models.py
index 0d3a8a2713..9f0997b014 100644
--- a/tests/aggregation/models.py
+++ b/tests/aggregation/models.py
@@ -43,3 +43,7 @@ class Store(models.Model):
 
     def __str__(self):
         return self.name
+
+
+class Employee(models.Model):
+    work_day_preferences = models.JSONField()
diff --git a/tests/aggregation/tests.py b/tests/aggregation/tests.py
index 86151000b5..8caefc060c 100644
--- a/tests/aggregation/tests.py
+++ b/tests/aggregation/tests.py
@@ -4,10 +4,11 @@ import re
 from decimal import Decimal
 
 from django.core.exceptions import FieldError
-from django.db import connection
+from django.db import NotSupportedError, connection
 from django.db.models import (
     Avg,
     Case,
+    CharField,
     Count,
     DateField,
     DateTimeField,
@@ -22,6 +23,7 @@ from django.db.models import (
     OuterRef,
     Q,
     StdDev,
+    StringAgg,
     Subquery,
     Sum,
     TimeField,
@@ -32,9 +34,11 @@ from django.db.models import (
     Window,
 )
 from django.db.models.expressions import Func, RawSQL
+from django.db.models.fields.json import KeyTextTransform
 from django.db.models.functions import (
     Cast,
     Coalesce,
+    Concat,
     Greatest,
     Least,
     Lower,
@@ -45,11 +49,11 @@ from django.db.models.functions import (
     TruncHour,
 )
 from django.test import TestCase
-from django.test.testcases import skipUnlessDBFeature
+from django.test.testcases import skipIfDBFeature, skipUnlessDBFeature
 from django.test.utils import Approximate, CaptureQueriesContext
 from django.utils import timezone
 
-from .models import Author, Book, Publisher, Store
+from .models import Author, Book, Employee, Publisher, Store
 
 
 class NowUTC(Now):
@@ -566,6 +570,28 @@ class AggregateTestCase(TestCase):
                 )
                 self.assertEqual(books["ratings"], expected_result)
 
+    @skipUnlessDBFeature("supports_aggregate_distinct_multiple_argument")
+    def test_distinct_on_stringagg(self):
+        books = Book.objects.aggregate(
+            ratings=StringAgg(Cast(F("rating"), CharField()), Value(","), distinct=True)
+        )
+        self.assertEqual(books["ratings"], "3,4,4.5,5")
+
+    @skipIfDBFeature("supports_aggregate_distinct_multiple_argument")
+    def test_raises_error_on_multiple_argument_distinct(self):
+        message = (
+            "StringAgg does not support distinct with multiple expressions on this "
+            "database backend."
+        )
+        with self.assertRaisesMessage(NotSupportedError, message):
+            Book.objects.aggregate(
+                ratings=StringAgg(
+                    Cast(F("rating"), CharField()),
+                    Value(","),
+                    distinct=True,
+                )
+            )
+
     def test_non_grouped_annotation_not_in_group_by(self):
         """
         An annotation not included in values() before an aggregate should be
@@ -1288,24 +1314,30 @@ class AggregateTestCase(TestCase):
             Book.objects.annotate(Max("id")).annotate(my_max=MyMax("id__max", "price"))
 
     def test_multi_arg_aggregate(self):
-        class MyMax(Max):
+        class MultiArgAgg(Max):
             output_field = DecimalField()
             arity = None
 
-            def as_sql(self, compiler, connection):
+            def as_sql(self, compiler, connection, **extra_context):
                 copy = self.copy()
-                copy.set_source_expressions(copy.get_source_expressions()[0:1] + [None])
-                return super(MyMax, copy).as_sql(compiler, connection)
+                # Most database backends do not support compiling multiple arguments on
+                # the Max aggregate, and that isn't what is being tested here anyway. To
+                # avoid errors, the extra argument is just dropped.
+                copy.set_source_expressions(
+                    copy.get_source_expressions()[0:1] + [None, None]
+                )
+
+                return super(MultiArgAgg, copy).as_sql(compiler, connection)
 
         with self.assertRaisesMessage(TypeError, "Complex aggregates require an alias"):
-            Book.objects.aggregate(MyMax("pages", "price"))
+            Book.objects.aggregate(MultiArgAgg("pages", "price"))
 
         with self.assertRaisesMessage(
             TypeError, "Complex annotations require an alias"
         ):
-            Book.objects.annotate(MyMax("pages", "price"))
+            Book.objects.annotate(MultiArgAgg("pages", "price"))
 
-        Book.objects.aggregate(max_field=MyMax("pages", "price"))
+        Book.objects.aggregate(max_field=MultiArgAgg("pages", "price"))
 
     def test_add_implementation(self):
         class MySum(Sum):
@@ -1318,6 +1350,8 @@ class AggregateTestCase(TestCase):
                 "function": self.function.lower(),
                 "expressions": sql,
                 "distinct": "",
+                "filter": "",
+                "order_by": "",
             }
             substitutions.update(self.extra)
             return self.template % substitutions, params
@@ -1351,7 +1385,13 @@ class AggregateTestCase(TestCase):
 
         # test overriding all parts of the template
         def be_evil(self, compiler, connection):
-            substitutions = {"function": "MAX", "expressions": "2", "distinct": ""}
+            substitutions = {
+                "function": "MAX",
+                "expressions": "2",
+                "distinct": "",
+                "filter": "",
+                "order_by": "",
+            }
             substitutions.update(self.extra)
             return self.template % substitutions, ()
 
@@ -1779,10 +1819,12 @@ class AggregateTestCase(TestCase):
                 Publisher.objects.none().aggregate(
                     sum_awards=Sum("num_awards"),
                     books_count=Count("book"),
+                    all_names=StringAgg("name", Value(",")),
                 ),
                 {
                     "sum_awards": None,
                     "books_count": 0,
+                    "all_names": None,
                 },
             )
         # Expression without empty_result_set_value forces queries to be
@@ -1874,6 +1916,12 @@ class AggregateTestCase(TestCase):
                 )
                 self.assertEqual(result["value"], 35)
 
+    def test_stringagg_default_value(self):
+        result = Author.objects.filter(age__gt=100).aggregate(
+            value=StringAgg("name", delimiter=Value(";"), default=Value("<empty>")),
+        )
+        self.assertEqual(result["value"], "<empty>")
+
     def test_aggregation_default_group_by(self):
         qs = (
             Publisher.objects.values("name")
@@ -2202,6 +2250,167 @@ class AggregateTestCase(TestCase):
                 with self.assertRaisesMessage(TypeError, msg):
                     super(function, func_instance).__init__(Value(1), Value(2))
 
+    def test_string_agg_requires_delimiter(self):
+        with self.assertRaises(TypeError):
+            Book.objects.aggregate(stringagg=StringAgg("name"))
+
+    def test_string_agg_escapes_delimiter(self):
+        values = Publisher.objects.aggregate(
+            stringagg=StringAgg("name", delimiter=Value("'"))
+        )
+
+        self.assertEqual(
+            values,
+            {
+                "stringagg": "Apress'Sams'Prentice Hall'Morgan Kaufmann'Jonno's House "
+                "of Books",
+            },
+        )
+
+    @skipUnlessDBFeature("supports_aggregate_order_by_clause")
+    def test_string_agg_order_by(self):
+        order_by_test_cases = (
+            (
+                F("original_opening").desc(),
+                "Books.com;Amazon.com;Mamma and Pappa's Books",
+            ),
+            (
+                F("original_opening").asc(),
+                "Mamma and Pappa's Books;Amazon.com;Books.com",
+            ),
+            (F("original_opening"), "Mamma and Pappa's Books;Amazon.com;Books.com"),
+            ("original_opening", "Mamma and Pappa's Books;Amazon.com;Books.com"),
+            ("-original_opening", "Books.com;Amazon.com;Mamma and Pappa's Books"),
+            (
+                Concat("original_opening", Value("@")),
+                "Mamma and Pappa's Books;Amazon.com;Books.com",
+            ),
+            (
+                Concat("original_opening", Value("@")).desc(),
+                "Books.com;Amazon.com;Mamma and Pappa's Books",
+            ),
+        )
+        for order_by, expected_output in order_by_test_cases:
+            with self.subTest(order_by=order_by, expected_output=expected_output):
+                values = Store.objects.aggregate(
+                    stringagg=StringAgg("name", delimiter=Value(";"), order_by=order_by)
+                )
+                self.assertEqual(values, {"stringagg": expected_output})
+
+    @skipIfDBFeature("supports_aggregate_order_by_clause")
+    def test_string_agg_order_by_is_not_supported(self):
+        message = (
+            "This database backend does not support specifying an order on aggregates."
+        )
+        with self.assertRaisesMessage(NotSupportedError, message):
+            Store.objects.aggregate(
+                stringagg=StringAgg(
+                    "name",
+                    delimiter=Value(";"),
+                    order_by="original_opening",
+                )
+            )
+
+    def test_string_agg_filter(self):
+        values = Book.objects.aggregate(
+            stringagg=StringAgg(
+                "name",
+                delimiter=Value(";"),
+                filter=Q(name__startswith="P"),
+            )
+        )
+
+        expected_values = {
+            "stringagg": "Practical Django Projects;"
+            "Python Web Development with Django;Paradigms of Artificial "
+            "Intelligence Programming: Case Studies in Common Lisp",
+        }
+        self.assertEqual(values, expected_values)
+
+    @skipUnlessDBFeature("supports_json_field", "supports_aggregate_order_by_clause")
+    def test_string_agg_jsonfield_order_by(self):
+        Employee.objects.bulk_create(
+            [
+                Employee(work_day_preferences={"Monday": "morning"}),
+                Employee(work_day_preferences={"Monday": "afternoon"}),
+            ]
+        )
+        values = Employee.objects.aggregate(
+            stringagg=StringAgg(
+                KeyTextTransform("Monday", "work_day_preferences"),
+                delimiter=Value(","),
+                order_by=KeyTextTransform(
+                    "Monday",
+                    "work_day_preferences",
+                ),
+                output_field=CharField(),
+            ),
+        )
+        self.assertEqual(values, {"stringagg": "afternoon,morning"})
+
+    def test_string_agg_filter_in_subquery(self):
+        aggregate = StringAgg(
+            "authors__name",
+            delimiter=Value(";"),
+            filter=~Q(authors__name__startswith="J"),
+        )
+        subquery = (
+            Book.objects.filter(
+                pk=OuterRef("pk"),
+            )
+            .annotate(agg=aggregate)
+            .values("agg")
+        )
+        values = list(
+            Book.objects.annotate(
+                agg=Subquery(subquery),
+            ).values_list("agg", flat=True)
+        )
+
+        expected_values = [
+            "Adrian Holovaty",
+            "Brad Dayley",
+            "Paul Bissex;Wesley J. Chun",
+            "Peter Norvig;Stuart Russell",
+            "Peter Norvig",
+            "" if connection.features.interprets_empty_strings_as_nulls else None,
+        ]
+
+        self.assertQuerySetEqual(expected_values, values, ordered=False)
+
+    @skipUnlessDBFeature("supports_aggregate_order_by_clause")
+    def test_order_by_in_subquery(self):
+        aggregate = StringAgg(
+            "authors__name",
+            delimiter=Value(";"),
+            order_by="authors__name",
+        )
+        subquery = (
+            Book.objects.filter(
+                pk=OuterRef("pk"),
+            )
+            .annotate(agg=aggregate)
+            .values("agg")
+        )
+        values = list(
+            Book.objects.annotate(
+                agg=Subquery(subquery),
+            )
+            .order_by("agg")
+            .values_list("agg", flat=True)
+        )
+
+        expected_values = [
+            "Adrian Holovaty;Jacob Kaplan-Moss",
+            "Brad Dayley",
+            "James Bennett",
+            "Jeffrey Forcier;Paul Bissex;Wesley J. Chun",
+            "Peter Norvig",
+            "Peter Norvig;Stuart Russell",
+        ]
+
+        self.assertEqual(expected_values, values)
+
 
 class AggregateAnnotationPruningTests(TestCase):
     @classmethod
diff --git a/tests/expressions_window/tests.py b/tests/expressions_window/tests.py
index fd9858ccf9..4480e15eb4 100644
--- a/tests/expressions_window/tests.py
+++ b/tests/expressions_window/tests.py
@@ -1720,14 +1720,14 @@ class WindowFunctionTests(TestCase):
         """Window expressions can't be used in an INSERT statement."""
         msg = (
             "Window expressions are not allowed in this query (salary=<Window: "
-            "Sum(Value(10000), order_by=OrderBy(F(pk), descending=False)) OVER ()"
+            "Sum(Value(10000)) OVER ()"
         )
         with self.assertRaisesMessage(FieldError, msg):
             Employee.objects.create(
                 name="Jameson",
                 department="Management",
                 hire_date=datetime.date(2007, 7, 1),
-                salary=Window(expression=Sum(Value(10000), order_by=F("pk").asc())),
+                salary=Window(expression=Sum(Value(10000))),
             )
 
     def test_window_expression_within_subquery(self):
@@ -2025,7 +2025,7 @@ class NonQueryWindowTests(SimpleTestCase):
     def test_invalid_order_by(self):
         msg = (
             "Window.order_by must be either a string reference to a field, an "
-            "expression, or a list or tuple of them."
+            "expression, or a list or tuple of them not {'-horse'}."
         )
         with self.assertRaisesMessage(ValueError, msg):
             Window(expression=Sum("power"), order_by={"-horse"})
diff --git a/tests/postgres_tests/test_aggregates.py b/tests/postgres_tests/test_aggregates.py
index ddd3b6bbd0..56544d99e5 100644
--- a/tests/postgres_tests/test_aggregates.py
+++ b/tests/postgres_tests/test_aggregates.py
@@ -1,3 +1,5 @@
+import warnings
+
 from django.db import transaction
 from django.db.models import (
     CharField,
@@ -11,17 +13,20 @@ from django.db.models import (
     Value,
     Window,
 )
-from django.db.models.fields.json import KeyTextTransform, KeyTransform
+from django.db.models.fields.json import KeyTransform
 from django.db.models.functions import Cast, Concat, LPad, Substr
 from django.test.utils import Approximate
 from django.utils import timezone
-from django.utils.deprecation import RemovedInDjango61Warning
+from django.utils.deprecation import RemovedInDjango61Warning, RemovedInDjango70Warning
 
 from . import PostgreSQLTestCase
 from .models import AggregateTestModel, HotelReservation, Room, StatTestModel
 
 try:
     from django.contrib.postgres.aggregates import (
+        StringAgg,  # RemovedInDjango70Warning.
+    )
+    from django.contrib.postgres.aggregates import (
         ArrayAgg,
         BitAnd,
         BitOr,
@@ -41,7 +46,6 @@ try:
         RegrSXY,
         RegrSYY,
         StatAggregate,
-        StringAgg,
     )
     from django.contrib.postgres.fields import ArrayField
 except ImportError:
@@ -94,7 +98,6 @@ class TestGeneralAggregate(PostgreSQLTestCase):
             BoolAnd("boolean_field"),
             BoolOr("boolean_field"),
             JSONBAgg("integer_field"),
-            StringAgg("char_field", delimiter=";"),
             BitXor("integer_field"),
         ]
         for aggregation in tests:
@@ -127,11 +130,6 @@ class TestGeneralAggregate(PostgreSQLTestCase):
                 JSONBAgg("integer_field", default=Value(["<empty>"], JSONField())),
                 ["<empty>"],
             ),
-            (StringAgg("char_field", delimiter=";", default="<empty>"), "<empty>"),
-            (
-                StringAgg("char_field", delimiter=";", default=Value("<empty>")),
-                "<empty>",
-            ),
             (BitXor("integer_field", default=0), 0),
         ]
         for aggregation, expected_result in tests:
@@ -158,8 +156,9 @@ class TestGeneralAggregate(PostgreSQLTestCase):
             self.assertEqual(values, {"arrayagg": [2, 1, 0, 0]})
         self.assertEqual(ctx.filename, __file__)
 
+    # RemovedInDjango61Warning: Remove this test
     def test_ordering_and_order_by_causes_error(self):
-        with self.assertWarns(RemovedInDjango61Warning):
+        with warnings.catch_warnings(record=True, action="always") as wm:
             with self.assertRaisesMessage(
                 TypeError,
                 "Cannot specify both order_by and ordering.",
@@ -173,6 +172,21 @@ class TestGeneralAggregate(PostgreSQLTestCase):
                     )
                 )
 
+        first_warning = wm[0]
+        self.assertEqual(first_warning.category, RemovedInDjango70Warning)
+        self.assertEqual(
+            "The PostgreSQL specific StringAgg function is deprecated. Use "
+            "django.db.models.aggregate.StringAgg instead.",
+            str(first_warning.message),
+        )
+
+        second_warning = wm[1]
+        self.assertEqual(second_warning.category, RemovedInDjango61Warning)
+        self.assertEqual(
+            "The ordering argument is deprecated. Use order_by instead.",
+            str(second_warning.message),
+        )
+
     def test_array_agg_charfield(self):
         values = AggregateTestModel.objects.aggregate(arrayagg=ArrayAgg("char_field"))
         self.assertEqual(values, {"arrayagg": ["Foo1", "Foo2", "Foo4", "Foo3"]})
@@ -425,66 +439,6 @@ class TestGeneralAggregate(PostgreSQLTestCase):
         )
         self.assertEqual(values, {"boolor": False})
 
-    def test_string_agg_requires_delimiter(self):
-        with self.assertRaises(TypeError):
-            AggregateTestModel.objects.aggregate(stringagg=StringAgg("char_field"))
-
-    def test_string_agg_delimiter_escaping(self):
-        values = AggregateTestModel.objects.aggregate(
-            stringagg=StringAgg("char_field", delimiter="'")
-        )
-        self.assertEqual(values, {"stringagg": "Foo1'Foo2'Foo4'Foo3"})
-
-    def test_string_agg_charfield(self):
-        values = AggregateTestModel.objects.aggregate(
-            stringagg=StringAgg("char_field", delimiter=";")
-        )
-        self.assertEqual(values, {"stringagg": "Foo1;Foo2;Foo4;Foo3"})
-
-    def test_string_agg_default_output_field(self):
-        values = AggregateTestModel.objects.aggregate(
-            stringagg=StringAgg("text_field", delimiter=";"),
-        )
-        self.assertEqual(values, {"stringagg": "Text1;Text2;Text4;Text3"})
-
-    def test_string_agg_charfield_order_by(self):
-        order_by_test_cases = (
-            (F("char_field").desc(), "Foo4;Foo3;Foo2;Foo1"),
-            (F("char_field").asc(), "Foo1;Foo2;Foo3;Foo4"),
-            (F("char_field"), "Foo1;Foo2;Foo3;Foo4"),
-            ("char_field", "Foo1;Foo2;Foo3;Foo4"),
-            ("-char_field", "Foo4;Foo3;Foo2;Foo1"),
-            (Concat("char_field", Value("@")), "Foo1;Foo2;Foo3;Foo4"),
-            (Concat("char_field", Value("@")).desc(), "Foo4;Foo3;Foo2;Foo1"),
-        )
-        for order_by, expected_output in order_by_test_cases:
-            with self.subTest(order_by=order_by, expected_output=expected_output):
-                values = AggregateTestModel.objects.aggregate(
-                    stringagg=StringAgg("char_field", delimiter=";", order_by=order_by)
-                )
-                self.assertEqual(values, {"stringagg": expected_output})
-
-    def test_string_agg_jsonfield_order_by(self):
-        values = AggregateTestModel.objects.aggregate(
-            stringagg=StringAgg(
-                KeyTextTransform("lang", "json_field"),
-                delimiter=";",
-                order_by=KeyTextTransform("lang", "json_field"),
-                output_field=CharField(),
-            ),
-        )
-        self.assertEqual(values, {"stringagg": "en;pl"})
-
-    def test_string_agg_filter(self):
-        values = AggregateTestModel.objects.aggregate(
-            stringagg=StringAgg(
-                "char_field",
-                delimiter=";",
-                filter=Q(char_field__endswith="3") | Q(char_field__endswith="1"),
-            )
-        )
-        self.assertEqual(values, {"stringagg": "Foo1;Foo3"})
-
     def test_orderable_agg_alternative_fields(self):
         values = AggregateTestModel.objects.aggregate(
             arrayagg=ArrayAgg("integer_field", order_by=F("char_field").asc())
@@ -593,48 +547,36 @@ class TestGeneralAggregate(PostgreSQLTestCase):
             ],
         )
 
-    def test_string_agg_array_agg_order_by_in_subquery(self):
+    def test_array_agg_order_by_in_subquery(self):
         stats = []
         for i, agg in enumerate(AggregateTestModel.objects.order_by("char_field")):
             stats.append(StatTestModel(related_field=agg, int1=i, int2=i + 1))
             stats.append(StatTestModel(related_field=agg, int1=i + 1, int2=i))
         StatTestModel.objects.bulk_create(stats)
 
-        for aggregate, expected_result in (
-            (
-                ArrayAgg("stattestmodel__int1", order_by="-stattestmodel__int2"),
-                [
-                    ("Foo1", [0, 1]),
-                    ("Foo2", [1, 2]),
-                    ("Foo3", [2, 3]),
-                    ("Foo4", [3, 4]),
-                ],
-            ),
-            (
-                StringAgg(
-                    Cast("stattestmodel__int1", CharField()),
-                    delimiter=";",
-                    order_by="-stattestmodel__int2",
-                ),
-                [("Foo1", "0;1"), ("Foo2", "1;2"), ("Foo3", "2;3"), ("Foo4", "3;4")],
-            ),
-        ):
-            with self.subTest(aggregate=aggregate.__class__.__name__):
-                subquery = (
-                    AggregateTestModel.objects.filter(
-                        pk=OuterRef("pk"),
-                    )
-                    .annotate(agg=aggregate)
-                    .values("agg")
-                )
-                values = (
-                    AggregateTestModel.objects.annotate(
-                        agg=Subquery(subquery),
-                    )
-                    .order_by("char_field")
-                    .values_list("char_field", "agg")
-                )
-                self.assertEqual(list(values), expected_result)
+        aggregate = ArrayAgg("stattestmodel__int1", order_by="-stattestmodel__int2")
+        expected_result = [
+            ("Foo1", [0, 1]),
+            ("Foo2", [1, 2]),
+            ("Foo3", [2, 3]),
+            ("Foo4", [3, 4]),
+        ]
+
+        subquery = (
+            AggregateTestModel.objects.filter(
+                pk=OuterRef("pk"),
+            )
+            .annotate(agg=aggregate)
+            .values("agg")
+        )
+        values = (
+            AggregateTestModel.objects.annotate(
+                agg=Subquery(subquery),
+            )
+            .order_by("char_field")
+            .values_list("char_field", "agg")
+        )
+        self.assertEqual(list(values), expected_result)
 
     def test_string_agg_array_agg_filter_in_subquery(self):
         StatTestModel.objects.bulk_create(
@@ -644,56 +586,31 @@ class TestGeneralAggregate(PostgreSQLTestCase):
                 StatTestModel(related_field=self.aggs[0], int1=2, int2=3),
             ]
         )
-        for aggregate, expected_result in (
-            (
-                ArrayAgg("stattestmodel__int1", filter=Q(stattestmodel__int2__gt=3)),
-                [("Foo1", [0, 1]), ("Foo2", None)],
-            ),
-            (
-                StringAgg(
-                    Cast("stattestmodel__int2", CharField()),
-                    delimiter=";",
-                    filter=Q(stattestmodel__int1__lt=2),
-                ),
-                [("Foo1", "5;4"), ("Foo2", None)],
-            ),
-        ):
-            with self.subTest(aggregate=aggregate.__class__.__name__):
-                subquery = (
-                    AggregateTestModel.objects.filter(
-                        pk=OuterRef("pk"),
-                    )
-                    .annotate(agg=aggregate)
-                    .values("agg")
-                )
-                values = (
-                    AggregateTestModel.objects.annotate(
-                        agg=Subquery(subquery),
-                    )
-                    .filter(
-                        char_field__in=["Foo1", "Foo2"],
-                    )
-                    .order_by("char_field")
-                    .values_list("char_field", "agg")
-                )
-                self.assertEqual(list(values), expected_result)
 
-    def test_string_agg_filter_in_subquery_with_exclude(self):
+        aggregate = ArrayAgg(
+            "stattestmodel__int1",
+            filter=Q(stattestmodel__int2__gt=3),
+        )
+        expected_result = [("Foo1", [0, 1]), ("Foo2", None)]
+
         subquery = (
-            AggregateTestModel.objects.annotate(
-                stringagg=StringAgg(
-                    "char_field",
-                    delimiter=";",
-                    filter=Q(char_field__endswith="1"),
-                )
+            AggregateTestModel.objects.filter(
+                pk=OuterRef("pk"),
             )
-            .exclude(stringagg="")
-            .values("id")
+            .annotate(agg=aggregate)
+            .values("agg")
         )
-        self.assertSequenceEqual(
-            AggregateTestModel.objects.filter(id__in=Subquery(subquery)),
-            [self.aggs[0]],
+        values = (
+            AggregateTestModel.objects.annotate(
+                agg=Subquery(subquery),
+            )
+            .filter(
+                char_field__in=["Foo1", "Foo2"],
+            )
+            .order_by("char_field")
+            .values_list("char_field", "agg")
         )
+        self.assertEqual(list(values), expected_result)
 
     def test_ordering_isnt_cleared_for_array_subquery(self):
         inner_qs = AggregateTestModel.objects.order_by("-integer_field")
@@ -729,11 +646,41 @@ class TestGeneralAggregate(PostgreSQLTestCase):
         tests = [ArrayAgg("integer_field"), JSONBAgg("integer_field")]
         for aggregation in tests:
             with self.subTest(aggregation=aggregation):
+                results = AggregateTestModel.objects.annotate(
+                    agg=aggregation
+                ).values_list("agg")
                 self.assertCountEqual(
-                    AggregateTestModel.objects.values_list(aggregation),
+                    results,
                     [([0],), ([1],), ([2],), ([0],)],
                 )
 
+    def test_string_agg_delimiter_deprecation(self):
+        msg = (
+            "delimiter: str will be resolved as a field reference instead "
+            'of a string literal on Django 7.0. Pass `delimiter=Value("\'")` to '
+            "preserve the previous behaviour."
+        )
+
+        with self.assertWarnsMessage(RemovedInDjango70Warning, msg) as ctx:
+            values = AggregateTestModel.objects.aggregate(
+                stringagg=StringAgg("char_field", delimiter="'")
+            )
+            self.assertEqual(values, {"stringagg": "Foo1'Foo2'Foo4'Foo3"})
+        self.assertEqual(ctx.filename, __file__)
+
+    def test_string_agg_deprecation(self):
+        msg = (
+            "The PostgreSQL specific StringAgg function is deprecated. Use "
+            "django.db.models.aggregate.StringAgg instead."
+        )
+
+        with self.assertWarnsMessage(RemovedInDjango70Warning, msg) as ctx:
+            values = AggregateTestModel.objects.aggregate(
+                stringagg=StringAgg("char_field", delimiter=Value("'"))
+            )
+            self.assertEqual(values, {"stringagg": "Foo1'Foo2'Foo4'Foo3"})
+        self.assertEqual(ctx.filename, __file__)
+
 
 class TestAggregateDistinct(PostgreSQLTestCase):
     @classmethod
@@ -742,20 +689,6 @@ class TestAggregateDistinct(PostgreSQLTestCase):
         AggregateTestModel.objects.create(char_field="Foo")
         AggregateTestModel.objects.create(char_field="Bar")
 
-    def test_string_agg_distinct_false(self):
-        values = AggregateTestModel.objects.aggregate(
-            stringagg=StringAgg("char_field", delimiter=" ", distinct=False)
-        )
-        self.assertEqual(values["stringagg"].count("Foo"), 2)
-        self.assertEqual(values["stringagg"].count("Bar"), 1)
-
-    def test_string_agg_distinct_true(self):
-        values = AggregateTestModel.objects.aggregate(
-            stringagg=StringAgg("char_field", delimiter=" ", distinct=True)
-        )
-        self.assertEqual(values["stringagg"].count("Foo"), 1)
-        self.assertEqual(values["stringagg"].count("Bar"), 1)
-
     def test_array_agg_distinct_false(self):
         values = AggregateTestModel.objects.aggregate(
             arrayagg=ArrayAgg("char_field", distinct=False)