Fixed error with avg aggregate when no matching rows - resolves #1012

Co-authored-by: Vaibhav Jain <jainva@google.com>

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.8.7 (unreleased)
+
+- Fixed error with `avg` aggregate when no matching rows
+
 ## 0.8.6 (2026-07-29)
 
 - Fixed buffer overflow with IVFFlat index build on 32-bit systems - [more info](https://github.com/pgvector/pgvector/issues/1006)

src/vector.c

@@ -1233,7 +1233,8 @@ vector_combine(PG_FUNCTION_ARGS)
 	{
 		n = n2;
 		dim = STATE_DIMS(statearray2);
-		CheckDim(dim);
+		if (dim != 0)
+			CheckDim(dim);
 		statedatums = CreateStateDatums(dim);
 		for (int i = 0; i < dim; i++)
 			statedatums[i + 1] = Float8GetDatum(statevalues2[i + 1]);

test/expected/vector_type.out

@@ -713,7 +713,11 @@ ERROR:  vector_combine: expected state array
 SELECT vector_combine('{0}', '{}');
 ERROR:  vector_combine: expected state array
 SELECT vector_combine('{0}', '{0}');
-ERROR:  vector must have at least 1 dimension
+ vector_combine 
+----------------
+ {0}
+(1 row)
+
 SELECT vector_combine('{0}', (SELECT array_agg(n) FROM generate_series(1, 16002) n));
 ERROR:  vector cannot have more than 16000 dimensions
 SELECT vector_combine((SELECT array_agg(n) FROM generate_series(1, 16002) n), '{0}');

test/t/018_aggregates.pl

@@ -42,6 +42,10 @@ sub test_aggregate
 	my $explain = $node->safe_psql("postgres", "EXPLAIN SELECT $agg(v) FROM tst;");
 	like($explain, qr/Partial Aggregate/);
 
+	# Test no matching rows
+	$res = $node->safe_psql("postgres", "SELECT $agg(v) FROM tst WHERE r1 < 0;");
+	is($res, '');
+
 	# Test halfvec
 	$res = $node->safe_psql("postgres", "SELECT $agg(v::halfvec) FROM tst;");
 	if ($agg eq 'avg')
@@ -55,6 +59,10 @@ sub test_aggregate
 		# Does not raise overflow error in this instance due to loss of precision
 		is($res, "[24576,24576,49152]");
 	}
+
+	# Test halfvec no matching rows
+	$res = $node->safe_psql("postgres", "SELECT $agg(v::halfvec) FROM tst WHERE r1 < 0;");
+	is($res, '');
 }
 
 test_aggregate('avg');