Add tests for decimal count distinct

datafusion/sqllogictest/test_files/aggregate.slt

@@ -2300,6 +2300,18 @@ select c2, avg(c1), arrow_typeof(avg(c1)) from d_table GROUP BY c2 ORDER BY c2
 A 110.0045 Decimal128(14, 7)
 B -100.0045 Decimal128(14, 7)
 
+# aggregate_decimal_count_distinct
+query I
+select count(DISTINCT c1) from d_table
+----
+20
+
+query TI
+select c2, count(DISTINCT c1) from d_table GROUP BY c2 ORDER BY c2
+----
+A 10
+B 10
+
 # Use PostgresSQL dialect
 statement ok
 set datafusion.sql_parser.dialect = 'Postgres';