diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/subplan/InlineSubplanInputForNestedTupleSourceRule.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/subplan/InlineSubplanInputForNestedTupleSourceRule.java
index 9f932a8..6220d06 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/subplan/InlineSubplanInputForNestedTupleSourceRule.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/subplan/InlineSubplanInputForNestedTupleSourceRule.java
@@ -638,9 +638,9 @@
             topJoinRef.setValue(ntsOp);
         }
         opRef.setValue(groupbyOp);
+        VariableUtilities.substituteVariables(groupbyOp, result.second, context);
         OperatorManipulationUtil.computeTypeEnvironmentBottomUp(groupbyOp, context);
 
-        VariableUtilities.substituteVariables(groupbyOp, result.second, context);
         replacedVarMap.putAll(result.second);
         return new Pair<>(true, replacedVarMap);
     }
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/SqlppExpressionToPlanTranslator.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/SqlppExpressionToPlanTranslator.java
index 65b0f03..1d226dd 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/SqlppExpressionToPlanTranslator.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/SqlppExpressionToPlanTranslator.java
@@ -345,7 +345,7 @@
     public Pair<ILogicalOperator, LogicalVariable> visit(JoinClause joinClause, Mutable<ILogicalOperator> leftInputRef)
             throws CompilationException {
         SourceLocation sourceLoc = joinClause.getSourceLocation();
-        if (joinClause.getJoinType() == JoinType.INNER) {
+        if (joinClause.getJoinType() == JoinType.INNER && !context.inSubplan()) {
             Mutable<ILogicalOperator> rightInputRef = uncorrelatedRightBranchStack.peek();
             Pair<ILogicalOperator, LogicalVariable> rightBranch =
                     generateUnnestForBinaryCorrelateRightBranch(joinClause, rightInputRef, false, null);
@@ -362,7 +362,7 @@
             filter.getInputs().add(conditionExprOpPair.second);
             filter.setSourceLocation(conditionExprOpPair.first.getSourceLocation());
             return new Pair<>(filter, rightBranch.second);
-        } else if (joinClause.getJoinType() == JoinType.LEFTOUTER) {
+        } else if (joinClause.getJoinType() == JoinType.INNER || joinClause.getJoinType() == JoinType.LEFTOUTER) {
             // Creates a subplan operator.
             SubplanOperator subplanOp = new SubplanOperator();
             subplanOp.getInputs().add(leftInputRef);
@@ -442,21 +442,22 @@
             ILogicalPlan subplan = new ALogicalPlanImpl(new MutableObject<>(aggOp));
             subplanOp.getNestedPlans().add(subplan);
 
-            // Outer unnest the aggregated var from the subplan.
-            LogicalVariable outerUnnestVar = context.newVar();
+            // Unnest the aggregated var from the subplan.
+            LogicalVariable unnestVar = context.newVar();
             VariableReferenceExpression aggVarRefExpr = new VariableReferenceExpression(aggVar);
             aggVarRefExpr.setSourceLocation(aggOp.getSourceLocation());
             Pair<ILogicalExpression, Mutable<ILogicalOperator>> pUnnestExpr =
                     makeUnnestExpression(aggVarRefExpr, new MutableObject<>(subplanOp));
-            LeftOuterUnnestOperator outerUnnestOp =
-                    new LeftOuterUnnestOperator(outerUnnestVar, new MutableObject<>(pUnnestExpr.first),
+            AbstractUnnestOperator unnestOp = joinClause.getJoinType() == JoinType.INNER
+                    ? new UnnestOperator(unnestVar, new MutableObject<>(pUnnestExpr.first))
+                    : new LeftOuterUnnestOperator(unnestVar, new MutableObject<>(pUnnestExpr.first),
                             translateLeftOuterMissingValue(joinClause.getOuterJoinMissingValueType()));
-            outerUnnestOp.getInputs().add(pUnnestExpr.second);
-            outerUnnestOp.setSourceLocation(aggOp.getSourceLocation());
-            currentTopOp = outerUnnestOp;
+            unnestOp.getInputs().add(pUnnestExpr.second);
+            unnestOp.setSourceLocation(aggOp.getSourceLocation());
+            currentTopOp = unnestOp;
 
             if (hasRightPosVar) {
-                VariableReferenceExpression outerUnnestVarRef1 = new VariableReferenceExpression(outerUnnestVar);
+                VariableReferenceExpression outerUnnestVarRef1 = new VariableReferenceExpression(unnestVar);
                 outerUnnestVarRef1.setSourceLocation(joinClause.getRightVariable().getSourceLocation());
                 ScalarFunctionCallExpression fieldAccessForRightUnnestVar = new ScalarFunctionCallExpression(
                         FunctionUtil.getFunctionInfo(BuiltinFunctions.FIELD_ACCESS_BY_INDEX),
@@ -464,7 +465,7 @@
                         new MutableObject<>(new ConstantExpression(new AsterixConstantValue(new AInt32(0)))));
                 fieldAccessForRightUnnestVar.setSourceLocation(joinClause.getRightVariable().getSourceLocation());
 
-                VariableReferenceExpression outerUnnestVarRef2 = new VariableReferenceExpression(outerUnnestVar);
+                VariableReferenceExpression outerUnnestVarRef2 = new VariableReferenceExpression(unnestVar);
                 outerUnnestVarRef2.setSourceLocation(joinClause.getPositionalVariable().getSourceLocation());
                 ScalarFunctionCallExpression fieldAccessForRightPosVar = new ScalarFunctionCallExpression(
                         FunctionUtil.getFunctionInfo(BuiltinFunctions.FIELD_ACCESS_BY_INDEX),
@@ -496,7 +497,7 @@
                 assignOp.setSourceLocation(joinClause.getRightVariable().getSourceLocation());
                 currentTopOp = assignOp;
             } else {
-                context.setVar(joinClause.getRightVariable(), outerUnnestVar);
+                context.setVar(joinClause.getRightVariable(), unnestVar);
             }
             return new Pair<>(currentTopOp, null);
         } else if (joinClause.getJoinType() == JoinType.RIGHTOUTER) {
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/TranslationContext.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/TranslationContext.java
index 33653ad..91629b6 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/TranslationContext.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/translator/TranslationContext.java
@@ -123,6 +123,13 @@
         }
     }
 
+    /*
+     * Whether the translation is inside a subplan
+     */
+    public boolean inSubplan() {
+        return !stack.isEmpty();
+    }
+
     /**
      * @return the variables produced by the top operator in a subplan.
      */
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/queries/subquery/query-ASTERIXDB-3006.sqlpp b/asterixdb/asterix-app/src/test/resources/optimizerts/queries/subquery/query-ASTERIXDB-3006.sqlpp
new file mode 100644
index 0000000..6bf64c4
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/queries/subquery/query-ASTERIXDB-3006.sqlpp
@@ -0,0 +1,38 @@
+/*
+ * 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.
+ */
+
+/*
+ * Description: This test case is to verify the fix for ASTERIXDB-3006
+ */
+
+drop dataverse test if exists;
+create dataverse test;
+use test;
+
+create dataset ds1(id int not unknown) open type primary key id;
+create dataset ds2(id int not unknown) open type primary key id;
+
+select value ds1
+from ds1
+where exists(
+   select 1
+   from ds1.a[*].b b
+   join ds2 on ds2.x[0].y = b
+)
+order by ds1.id;
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/subquery/query-ASTERIXDB-3006.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/subquery/query-ASTERIXDB-3006.plan
new file mode 100644
index 0000000..a5264a9
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/subquery/query-ASTERIXDB-3006.plan
@@ -0,0 +1,49 @@
+-- DISTRIBUTE_RESULT  |PARTITIONED|
+  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+    -- STREAM_PROJECT  |PARTITIONED|
+      -- SORT_MERGE_EXCHANGE [$$64(ASC) ]  |PARTITIONED|
+        -- STREAM_PROJECT  |PARTITIONED|
+          -- STREAM_SELECT  |PARTITIONED|
+            -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+              -- SORT_GROUP_BY[$$78]  |PARTITIONED|
+                      {
+                        -- AGGREGATE  |LOCAL|
+                          -- NESTED_TUPLE_SOURCE  |LOCAL|
+                      }
+                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                  -- PRE_CLUSTERED_GROUP_BY[$$48]  |PARTITIONED|
+                          {
+                            -- AGGREGATE  |LOCAL|
+                              -- STREAM_SELECT  |LOCAL|
+                                -- NESTED_TUPLE_SOURCE  |LOCAL|
+                          }
+                    -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                      -- STREAM_PROJECT  |PARTITIONED|
+                        -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                          -- HYBRID_HASH_JOIN [$$48][$$61]  |PARTITIONED|
+                            -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                              -- DATASOURCE_SCAN (test.ds1)  |PARTITIONED|
+                                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                  -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
+                            -- HASH_PARTITION_EXCHANGE [$$61]  |PARTITIONED|
+                              -- ASSIGN  |PARTITIONED|
+                                -- STREAM_PROJECT  |PARTITIONED|
+                                  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                    -- HYBRID_HASH_JOIN [$$b][$$51]  |PARTITIONED|
+                                      -- HASH_PARTITION_EXCHANGE [$$b]  |PARTITIONED|
+                                        -- STREAM_PROJECT  |PARTITIONED|
+                                          -- UNNEST  |PARTITIONED|
+                                            -- STREAM_PROJECT  |PARTITIONED|
+                                              -- ASSIGN  |PARTITIONED|
+                                                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                  -- DATASOURCE_SCAN (test.ds1)  |PARTITIONED|
+                                                    -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                      -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
+                                      -- HASH_PARTITION_EXCHANGE [$$51]  |PARTITIONED|
+                                        -- STREAM_PROJECT  |PARTITIONED|
+                                          -- ASSIGN  |PARTITIONED|
+                                            -- STREAM_PROJECT  |PARTITIONED|
+                                              -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                -- DATASOURCE_SCAN (test.ds2)  |PARTITIONED|
+                                                  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                    -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.1.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.1.ddl.sqlpp
new file mode 100644
index 0000000..bb5c8f5
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.1.ddl.sqlpp
@@ -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.
+ */
+
+/*
+ * Description: This test case is to verify the fix for ASTERIXDB-3006
+ */
+
+drop dataverse test if exists;
+create dataverse test;
+use test;
+
+create dataset ds1(id int not unknown) open type primary key id;
+create dataset ds2(id int not unknown) open type primary key id;
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.2.update.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.2.update.sqlpp
new file mode 100644
index 0000000..fd8e76b
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.2.update.sqlpp
@@ -0,0 +1,31 @@
+/*
+ * 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.
+ */
+
+use test;
+
+insert into ds1 ([
+  { "id": 1, "a": [ { "b": 1 }, { "b": 11 }, { "b": 111 } ] },
+  { "id": 2, "a": [ { "b": 2 }, { "b": 22 }, { "b": 222 } ] },
+  { "id": 3, "a": [ { "b": 3 }, { "b": 33 }, { "b": 333 } ] }
+]);
+
+insert into ds2 ([
+  { "id": 101, "x": [ { "y": 33 }, { "y": 11 } ] },
+  { "id": 102, "x": [ { "y": 22 }, { "y": 11 } ] }
+]);
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.3.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.3.query.sqlpp
new file mode 100644
index 0000000..ad662ba
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.3.query.sqlpp
@@ -0,0 +1,32 @@
+/*
+ * 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.
+ */
+
+/*
+ * Test inner join inside a subquery
+ */
+use test;
+
+select value ds1
+from ds1
+where exists(
+   select 1
+   from ds1.a[*].b b
+   join ds2 on ds2.x[0].y = b
+)
+order by ds1.id;
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.3.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.3.adm
new file mode 100644
index 0000000..99fe65f
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/subquery/query-ASTERIXDB-3006/query-ASTERIXDB-3006.3.adm
@@ -0,0 +1,2 @@
+{ "id": 2, "a": [ { "b": 2 }, { "b": 22 }, { "b": 222 } ] }
+{ "id": 3, "a": [ { "b": 3 }, { "b": 33 }, { "b": 333 } ] }
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
index c1aed2a..48b10ef 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
@@ -11374,6 +11374,11 @@
         <output-dir compare="Text">query-ASTERIXDB-2845</output-dir>
       </compilation-unit>
     </test-case>
+    <test-case FilePath="subquery">
+      <compilation-unit name="query-ASTERIXDB-3006">
+        <output-dir compare="Text">query-ASTERIXDB-3006</output-dir>
+      </compilation-unit>
+    </test-case>
   </test-group>
   <test-group name="subset-collection">
     <test-case FilePath="subset-collection">