builtins: implement ST_MemCollect and ST_MemUnion

These are implemented as aliases for ST_Collect and ST_Union. In PostGIS
these are memory-optimized versions, but for now it should be sufficient
to simply make them functional.

Release justification: low risk, high benefit changes to existing functionality

Release note (sql change): Implement the geometry aggregate builtins
`ST_MemCollect` and `ST_MemUnion`.

docs/generated/sql/aggregates.md

@@ -197,6 +197,10 @@
 </span></td></tr>
 <tr><td><a name="st_makeline"></a><code>st_makeline(arg1: geometry) &rarr; geometry</code></td><td><span class="funcdesc"><p>Forms a LineString from Point, MultiPoint or LineStrings. Other shapes will be ignored.</p>
 </span></td></tr>
+<tr><td><a name="st_memcollect"></a><code>st_memcollect(arg1: geometry) &rarr; geometry</code></td><td><span class="funcdesc"><p>Collects geometries into a GeometryCollection or multi-type as appropriate.</p>
+</span></td></tr>
+<tr><td><a name="st_memunion"></a><code>st_memunion(arg1: geometry) &rarr; geometry</code></td><td><span class="funcdesc"><p>Applies a spatial union to the geometries provided.</p>
+</span></td></tr>
 <tr><td><a name="st_union"></a><code>st_union(arg1: geometry) &rarr; geometry</code></td><td><span class="funcdesc"><p>Applies a spatial union to the geometries provided.</p>
 </span></td></tr>
 <tr><td><a name="stddev"></a><code>stddev(arg1: <a href="decimal.html">decimal</a>) &rarr; <a href="decimal.html">decimal</a></code></td><td><span class="funcdesc"><p>Calculates the standard deviation of the selected values.</p>

pkg/sql/logictest/testdata/logic_test/geospatial

@@ -4327,6 +4327,11 @@ SELECT ST_AsEWKT(ST_Union(g::geometry)) FROM ( VALUES (NULL), ('POINT(1 0)'), ('
 ----
 LINESTRING (0 0, 5 0)
 
+query T
+SELECT ST_AsEWKT(ST_MemUnion(g::geometry)) FROM ( VALUES (NULL), ('POINT(1 0)'), ('LINESTRING(0 0, 5 0)')) tbl(g)
+----
+LINESTRING (0 0, 5 0)
+
 query T
 SELECT ST_AsEWKT(ST_Collect(g::geometry)) FROM ( VALUES (NULL) ) tbl(g)
 ----
@@ -4365,6 +4370,10 @@ SELECT ST_AsEWKT(ST_Collect(g::geometry)) FROM ( VALUES ('GEOMETRYCOLLECTION (PO
 ----
 GEOMETRYCOLLECTION (GEOMETRYCOLLECTION (POINT (1 1)), GEOMETRYCOLLECTION (POINT (2 2)))
 
+query T
+SELECT ST_AsEWKT(ST_MemCollect(g::geometry)) FROM ( VALUES (NULL), ('POINT (1 1)'), ('POINT EMPTY'), ('POINT (2 2)')) tbl(g)
+----
+MULTIPOINT (1 1, EMPTY, 2 2)
 
 query T
 SELECT ST_AsEWKT(

pkg/sql/opt/optbuilder/groupby.go

@@ -825,11 +825,11 @@ func (b *Builder) constructAggregate(name string, args []opt.ScalarExpr) opt.Sca
 		return b.factory.ConstructVarPop(args[0])
 	case "st_makeline":
 		return b.factory.ConstructSTMakeLine(args[0])
-	case "st_collect":
+	case "st_collect", "st_memcollect":
 		return b.factory.ConstructSTCollect(args[0])
 	case "st_extent":
 		return b.factory.ConstructSTExtent(args[0])
-	case "st_union":
+	case "st_union", "st_memunion":
 		return b.factory.ConstructSTUnion(args[0])
 	case "xor_agg":
 		return b.factory.ConstructXorAgg(args[0])

pkg/sql/sem/builtins/aggregate_builtins.go

@@ -400,42 +400,10 @@ var aggregates = map[string]builtinDefinition{
 			tree.VolatilityImmutable,
 		),
 	),
-	"st_union": makeBuiltin(
-		tree.FunctionProperties{
-			Class:                   tree.AggregateClass,
-			NullableArgs:            true,
-			AvailableOnPublicSchema: true,
-		},
-		makeAggOverload(
-			[]*types.T{types.Geometry},
-			types.Geometry,
-			func(
-				params []*types.T, evalCtx *tree.EvalContext, arguments tree.Datums,
-			) tree.AggregateFunc {
-				return &stUnionAgg{}
-			},
-			infoBuilder{
-				info: "Applies a spatial union to the geometries provided.",
-			}.String(),
-			tree.VolatilityImmutable,
-		),
-	),
-	"st_collect": makeBuiltin(
-		tree.FunctionProperties{
-			Class:                   tree.AggregateClass,
-			NullableArgs:            true,
-			AvailableOnPublicSchema: true,
-		},
-		makeAggOverload(
-			[]*types.T{types.Geometry},
-			types.Geometry,
-			newSTCollectAgg,
-			infoBuilder{
-				info: "Collects geometries into a GeometryCollection or multi-type as appropriate.",
-			}.String(),
-			tree.VolatilityImmutable,
-		),
-	),
+	"st_union":      makeSTUnionBuiltin(),
+	"st_memunion":   makeSTUnionBuiltin(),
+	"st_collect":    makeSTCollectBuiltin(),
+	"st_memcollect": makeSTCollectBuiltin(),
 
 	AnyNotNull: makePrivate(makeBuiltin(aggProps(),
 		makeAggOverloadWithReturnType(
@@ -627,6 +595,48 @@ func makeStdDevBuiltin() builtinDefinition {
 	)
 }
 
+func makeSTCollectBuiltin() builtinDefinition {
+	return makeBuiltin(
+		tree.FunctionProperties{
+			Class:                   tree.AggregateClass,
+			NullableArgs:            true,
+			AvailableOnPublicSchema: true,
+		},
+		makeAggOverload(
+			[]*types.T{types.Geometry},
+			types.Geometry,
+			newSTCollectAgg,
+			infoBuilder{
+				info: "Collects geometries into a GeometryCollection or multi-type as appropriate.",
+			}.String(),
+			tree.VolatilityImmutable,
+		),
+	)
+}
+
+func makeSTUnionBuiltin() builtinDefinition {
+	return makeBuiltin(
+		tree.FunctionProperties{
+			Class:                   tree.AggregateClass,
+			NullableArgs:            true,
+			AvailableOnPublicSchema: true,
+		},
+		makeAggOverload(
+			[]*types.T{types.Geometry},
+			types.Geometry,
+			func(
+				params []*types.T, evalCtx *tree.EvalContext, arguments tree.Datums,
+			) tree.AggregateFunc {
+				return &stUnionAgg{}
+			},
+			infoBuilder{
+				info: "Applies a spatial union to the geometries provided.",
+			}.String(),
+			tree.VolatilityImmutable,
+		),
+	)
+}
+
 type stMakeLineAgg struct {
 	flatCoords []float64
 	layout     geom.Layout