diff --git a/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java b/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java
index 92f8ec7cb336..a352ca54e060 100644
--- a/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java
+++ b/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java
@@ -75,6 +75,7 @@
 import org.apache.calcite.sql.SqlMerge;
 import org.apache.calcite.sql.SqlNode;
 import org.apache.calcite.sql.SqlNodeList;
+import org.apache.calcite.sql.SqlOperator;
 import org.apache.calcite.sql.SqlSampleSpec;
 import org.apache.calcite.sql.SqlSelect;
 import org.apache.calcite.sql.SqlTableRef;
@@ -1272,8 +1273,9 @@ private static SqlCall as(SqlNode e, String alias) {
 
   public Result visit(Uncollect e) {
     final Result x = visitInput(e, 0);
-    final SqlNode unnestNode =
-        SqlStdOperatorTable.UNNEST.createCall(POS, x.asStatement());
+    final SqlOperator operator =
+        e.withOrdinality ? SqlStdOperatorTable.UNNEST_WITH_ORDINALITY : SqlStdOperatorTable.UNNEST;
+    final SqlNode unnestNode = operator.createCall(POS, x.asStatement());
     final List<SqlNode> operands =
         createAsFullOperands(e.getRowType(), unnestNode,
             requireNonNull(x.neededAlias,
diff --git a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
index e8632f7a80d5..739153345b11 100644
--- a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
+++ b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
@@ -6376,6 +6376,31 @@ private void checkLiteral2(String expression, String expected) {
     sql(sql).ok(expected);
   }
 
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-6231">[CALCITE-6231]
+   * JDBC adapter generates "UNNEST" when it should generate "UNNEST ... WITH ORDINALITY" </a>.
+   */
+  @Test void testUncollectExplicitAliasWithOrd() {
+    final String sql = "select did + 1\n"
+        + "from unnest(select collect(\"department_id\") as deptid \n"
+        + "from \"department\") with ordinality as t(did, pos)";
+
+    final String expected = "SELECT \"DEPTID\" + 1\n"
+        + "FROM UNNEST (SELECT COLLECT(\"department_id\") AS \"DEPTID\"\n"
+        + "FROM \"foodmart\".\"department\") WITH ORDINALITY AS \"t0\" (\"DEPTID\", \"ORDINALITY\")";
+    sql(sql).ok(expected);
+  }
+
+  @Test void testUncollectImplicitAliasWithOrd() {
+    final String sql = "select did + 1\n"
+        + "from unnest(select collect(\"department_id\") \n"
+        + "from \"department\") with ordinality as t(did, pos)";
+
+    final String expected = "SELECT \"col_0\" + 1\n"
+        + "FROM UNNEST (SELECT COLLECT(\"department_id\")\n"
+        + "FROM \"foodmart\".\"department\") WITH ORDINALITY AS \"t0\" (\"col_0\", \"ORDINALITY\")";
+    sql(sql).ok(expected);
+  }
 
   @Test void testWithinGroup1() {
     final String query = "select \"product_class_id\", collect(\"net_weight\") "