diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1047.aql b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1047.aql
new file mode 100644
index 0000000..4210fc3
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1047.aql
@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/**
+ * This query is to verify the fix of ASTERIXDB-1047.
+ */
+
+drop dataverse test if exists;
+create dataverse test;
+use dataverse test;
+
+create type DBLPType as open {
+  id: int64,
+  dblpid: string,
+  title: string,
+  authors: string,
+  misc: string
+}
+
+create dataset DBLP(DBLPType) primary key id;
+
+
+(for $d in dataset DBLP where $d.id = 1 return $d)
+  union
+(for $d in dataset DBLP where $d.authors = "Alfred V. Aho John E. Hopcroft Jeffrey D. Ullman" return $d);
diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-2.aql b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-2.aql
new file mode 100644
index 0000000..82d1430
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-2.aql
@@ -0,0 +1,28 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/**
+ * This query is to verify the fix of ASTERIXDB-1205.
+ */
+
+let $aa := [{"fa":1, "fb":1}, {"fa":2, "fb":1}]
+let $bb := [{"fa":1, "fb":0}, {"fa":1, "fb":1}, {"fa":3, "fb":1}]
+
+for $tt in ($aa union $bb)
+order by $tt.fa, $tt.fb
+return $tt;
diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-3.aql b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-3.aql
new file mode 100644
index 0000000..2ab92dc
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-3.aql
@@ -0,0 +1,25 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/**
+ * This query is to verify the fix of ASTERIXDB-1205.
+ */
+
+let $aa := [{"fa":1, "fb":1}, {"fa":2, "fb":1}]
+let $bb := [{"fa":1, "fb":0}, {"fa":1, "fb":1}, {"fa":3, "fb":1}]
+return $aa union $bb;
\ No newline at end of file
diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-4.aql b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-4.aql
new file mode 100644
index 0000000..48f7c2a
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205-4.aql
@@ -0,0 +1,30 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/**
+ * This query is to verify the fix of ASTERIXDB-1205.
+ */
+
+let $aa := [{"fa":1, "fb":1}, {"fa":2, "fb":1}]
+let $bb := [{"fa":1, "fb":0}, {"fa":1, "fb":1}, {"fa":3, "fb":1}]
+let $dd := [{"fa":4, "fb":5}, {"fa":6, "fb":7}]
+let $ccc := $aa union $bb union $dd
+
+for $tt in $ccc
+order by $tt.fa, $tt.fb
+return $tt;
\ No newline at end of file
diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205.aql b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205.aql
new file mode 100644
index 0000000..763aba1
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/query-ASTERIXDB-1205.aql
@@ -0,0 +1,29 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/**
+ * This query is to verify the fix of ASTERIXDB-1205.
+ */
+
+let $aa := [{"fa":1, "fb":1}, {"fa":2, "fb":1}]
+let $bb := [{"fa":1, "fb":0}, {"fa":1, "fb":1}, {"fa":3, "fb":1}]
+let $ccc := $aa union $bb
+
+for $tt in $ccc
+order by $tt.fa, $tt.fb
+return $tt;
diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset.aql b/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset.aql
new file mode 100644
index 0000000..7a55ee5
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset.aql
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+drop dataverse TinySocial if exists;
+create dataverse TinySocial;
+use dataverse TinySocial;
+
+create type FacebookUserType as open {
+        id: int
+}
+
+create dataset FacebookUsers(FacebookUserType)
+primary key id;
+
+create dataset FacebookUsers2(FacebookUserType)
+primary key id;
+
+
+let $c := dataset("FacebookUsers") union dataset("FacebookUsers2")
+for $res in $c order by $res.id return $res
diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset2.aql b/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset2.aql
new file mode 100644
index 0000000..049652f
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset2.aql
@@ -0,0 +1,33 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+drop dataverse TinySocial if exists;
+create dataverse TinySocial;
+use dataverse TinySocial;
+
+create type FacebookUserType as open {
+        id: int
+}
+
+create dataset FacebookUsers(FacebookUserType)
+primary key id;
+
+create dataset FacebookUsers2(FacebookUserType)
+primary key id;
+
+dataset("FacebookUsers") union dataset("FacebookUsers2");
diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset3.aql b/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset3.aql
new file mode 100644
index 0000000..edb429f
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/union_dataset3.aql
@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+drop dataverse TinySocial if exists;
+create dataverse TinySocial;
+use dataverse TinySocial;
+
+create type FacebookUserType as open {
+        id: int
+}
+
+create dataset FacebookUsers(FacebookUserType)
+primary key id;
+
+create dataset FacebookUsers2(FacebookUserType)
+primary key id;
+
+
+for $res in (dataset("FacebookUsers") union dataset("FacebookUsers2"))
+order by $res.id return $res
diff --git a/asterix-app/src/test/resources/optimizerts/queries/union/union_query.aql b/asterix-app/src/test/resources/optimizerts/queries/union/union_query.aql
new file mode 100644
index 0000000..3e6ebaf
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/queries/union/union_query.aql
@@ -0,0 +1,41 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+drop dataverse TinySocial if exists;
+create dataverse TinySocial;
+use dataverse TinySocial;
+
+create type FacebookUserType as open {
+        id: int
+}
+
+create type FacebookMessageType as open {
+        message-id: int
+}
+
+create dataset FacebookUsers(FacebookUserType)
+primary key id;
+
+create dataset FacebookMessages(FacebookMessageType)
+primary key message-id;
+
+let $t1 := for $t in dataset FacebookUsers return $t.id
+let $t2 := for $s in dataset FacebookMessages return $s.message-id
+let $c := $t1 union $t2
+for $res in $c distinct by $res order by $res return $res