Fix Aggregate IndexError on a SQL query that matched nothing across shards (#1139)

test/python/testdatabase/testsql.py

@@ -5,6 +5,7 @@ SQL module tests
 import unittest
 
 from txtai.database import DatabaseFactory, SQL, SQLError
+from txtai.database.sql import Aggregate
 
 
 class TestSQL(unittest.TestCase):
@@ -312,6 +313,21 @@ class TestSQL(unittest.TestCase):
         self.assertSql("where", prefix + "where f(id) = b(id)", "f(s.id) = b(s.id)")
         self.assertSql("where", prefix + "WHERE f(id)", "f(s.id)")
 
+    def testAggregateEmptyResults(self):
+        """
+        Test Aggregate returns empty results for a SQL query that matched nothing
+        (e.g. a sharded query with zero hits across all shards) instead of crashing.
+        """
+
+        aggregate = Aggregate()
+
+        # SQL query, no results across shards - must not raise IndexError
+        self.assertEqual(aggregate("select id, text, score from txtai where similar('x')", []), [])
+        # Non-SQL query with no results stays consistent
+        self.assertEqual(aggregate("plain text query", []), [])
+        # SQL query with results still aggregates as before
+        self.assertEqual(aggregate("select count(*) from txtai", [{"count(*)": 1}, {"count(*)": 2}]), [{"count(*)": 3}])
+
     def assertSql(self, clause, query, expected):
         """
         Helper method to assert a query clause is as expected.