[CALCITE-4833] Complex nested correlated subquery failed.

core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java

@@ -4940,6 +4940,40 @@ ImmutableList<RelNode> retrieveCursors() {
       }
     }
 
+    /** Tries to simplify case:
+     *  select t1.a FROM emps t1 JOIN emps t2 ON (SELECT t2.a) _compare opeartor_ val;
+     *  The idea is to transform such a case into equivalent:
+     *  select t1.a FROM emps t1 JOIN emps t2 ON t2.a _compare opeartor_ val;
+     */
+    private @Nullable RexNode simplifyOnWithSelectInConditions(SqlNode expr) {
+      if (!(expr instanceof SqlBasicCall)) {
+        return null;
+      }
+      // (select t2.a) _compare opeartor_ val
+      SqlBasicCall call0 = (SqlBasicCall) expr;
+      if (call0.operandCount() != 2 || !(call0.operand(0) instanceof SqlBasicCall)) {
+        return null;
+      }
+      // left side i.e. (select t2.a)
+      SqlBasicCall selectCall = call0.operand(0);
+      if (selectCall.operandCount() != 1 || !(selectCall.getOperands()[0] instanceof SqlSelect)) {
+        return null;
+      }
+      // select t2.a
+      @Nullable SqlSelect colExpr = (SqlSelect) selectCall.getOperands()[0];
+      // empty from case, only 1 operand in current case possible
+      if (colExpr == null || colExpr.getFrom() != null || colExpr.getSelectList().size() != 1) {
+        return null;
+      }
+      // a
+      SqlNode selectParam = colExpr.getSelectList().get(0);
+      SqlNode op2 = call0.operand(1);
+      RexNode exp0 = convertExpression(selectParam);
+      RexNode exp1 = convertExpression(op2);
+      RexNode rex0 = rexBuilder.makeCall(call0.getOperator(), exp0, exp1);
+      return rex0;
+    }
+
     @Override public RexNode convertExpression(SqlNode expr) {
       // If we're in aggregation mode and this is an expression in the
       // GROUP BY clause, return a reference to the field.
@@ -4974,6 +5008,16 @@ ImmutableList<RelNode> retrieveCursors() {
         final SqlNode query;
         final RelRoot root;
         switch (kind) {
+        case LESS_THAN:
+        case GREATER_THAN:
+        case LESS_THAN_OR_EQUAL:
+        case GREATER_THAN_OR_EQUAL:
+        case EQUALS:
+          RexNode res = simplifyOnWithSelectInConditions(expr);
+          if (res != null) {
+            return res;
+          }
+          break;
         case IN:
         case NOT_IN:
         case SOME:

core/src/test/java/org/apache/calcite/test/enumerable/EnumerableCorrelateTest.java

@@ -168,6 +168,102 @@ class EnumerableCorrelateTest {
             "empid=200");
   }
 
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-4833">[CALCITE-4833]
+   * Complex nested correlated subquery failed</a>.
+   */
+  @Test void complexNestedCorrelatedSubquery() {
+    String sql = "SELECT t1.empid FROM emps t1 LEFT JOIN emps t2 ON (SELECT t2.empid)<=101";
+
+    tester(false, new HrSchema())
+        .query(sql)
+        .explainContains(""
+            + "EnumerableCalc(expr#0..1=[{inputs}], empid=[$t0])\n"
+            + "  EnumerableNestedLoopJoin(condition=[true], joinType=[left])\n"
+            + "    EnumerableCalc(expr#0..4=[{inputs}], empid=[$t0])\n"
+            + "      EnumerableTableScan(table=[[s, emps]])\n"
+            + "    EnumerableCalc(expr#0..4=[{inputs}], expr#5=[101], expr#6=[<=($t0, $t5)], $f5=[$t6], $condition=[$t6])\n"
+            + "      EnumerableTableScan(table=[[s, emps]])\n\n")
+        .returnsUnordered(
+            "empid=100",
+            "empid=110",
+            "empid=150",
+            "empid=200");
+
+    sql = "SELECT t1.empid FROM emps t1 LEFT JOIN emps t2 ON (SELECT t2.empid)<101";
+
+    tester(false, new HrSchema())
+        .query(sql)
+        .explainContains(""
+            + "EnumerableCalc(expr#0..1=[{inputs}], empid=[$t0])\n"
+            + "  EnumerableNestedLoopJoin(condition=[true], joinType=[left])\n"
+            + "    EnumerableCalc(expr#0..4=[{inputs}], empid=[$t0])\n"
+            + "      EnumerableTableScan(table=[[s, emps]])\n"
+            + "    EnumerableCalc(expr#0..4=[{inputs}], expr#5=[101], expr#6=[<($t0, $t5)], $f5=[$t6], $condition=[$t6])\n"
+            + "      EnumerableTableScan(table=[[s, emps]])\n\n")
+        .returnsUnordered(
+            "empid=100",
+            "empid=110",
+            "empid=150",
+            "empid=200");
+
+    sql = "SELECT t1.empid FROM emps t1 LEFT JOIN emps t2 ON (SELECT t2.empid)>150";
+
+    tester(false, new HrSchema())
+        .query(sql)
+        .explainContains(""
+            + "EnumerableCalc(expr#0..1=[{inputs}], empid=[$t0])\n"
+            + "  EnumerableNestedLoopJoin(condition=[true], joinType=[left])\n"
+            + "    EnumerableCalc(expr#0..4=[{inputs}], empid=[$t0])\n"
+            + "      EnumerableTableScan(table=[[s, emps]])\n"
+            + "    EnumerableCalc(expr#0..4=[{inputs}], expr#5=[150], expr#6=[>($t0, $t5)], $f5=[$t6], $condition=[$t6])\n"
+            + "      EnumerableTableScan(table=[[s, emps]])\n\n")
+        .returnsUnordered(
+            "empid=100",
+            "empid=110",
+            "empid=150",
+            "empid=200");
+
+    sql = "SELECT t1.empid FROM emps t1 LEFT JOIN emps t2 ON (SELECT t2.empid)=150";
+
+    tester(false, new HrSchema())
+        .query(sql)
+        .explainContains(""
+            + "EnumerableCalc(expr#0..1=[{inputs}], empid=[$t0])\n" +
+            "  EnumerableNestedLoopJoin(condition=[true], joinType=[left])\n" +
+            "    EnumerableCalc(expr#0..4=[{inputs}], empid=[$t0])\n" +
+            "      EnumerableTableScan(table=[[s, emps]])\n" +
+            "    EnumerableCalc(expr#0..4=[{inputs}], expr#5=[150], expr#6=[=($t0, $t5)], empid=[$t0], $condition=[$t6])\n" +
+            "      EnumerableTableScan(table=[[s, emps]])\n\n")
+        .returnsUnordered(
+            "empid=100",
+            "empid=110",
+            "empid=150",
+            "empid=200");
+
+    sql = "SELECT t1.empid FROM emps t1 LEFT JOIN emps t2 ON (SELECT t2.empid)=(select 100 + 50)";
+
+    tester(false, new HrSchema())
+        .query(sql)
+        .explainContains(""
+            + "EnumerableCalc(expr#0..2=[{inputs}], empid=[$t0])\n"
+            + "  EnumerableNestedLoopJoin(condition=[true], joinType=[left])\n"
+            + "    EnumerableCalc(expr#0..4=[{inputs}], empid=[$t0])\n"
+            + "      EnumerableTableScan(table=[[s, emps]])\n"
+            + "    EnumerableCalc(expr#0..1=[{inputs}], expr#2=[CAST($t0):INTEGER], empid=[$t1], $f0=[$t2])\n"
+            + "      EnumerableHashJoin(condition=[=($0, $1)], joinType=[inner])\n"
+            + "        EnumerableAggregate(group=[{}], agg#0=[SINGLE_VALUE($0)])\n"
+            + "          EnumerableCalc(expr#0=[{inputs}], expr#1=[100], expr#2=[50], expr#3=[+($t1, $t2)], EXPR$0=[$t3])\n"
+            + "            EnumerableValues(tuples=[[{ 0 }]])\n"
+            + "        EnumerableCalc(expr#0..4=[{inputs}], empid=[$t0])\n"
+            + "          EnumerableTableScan(table=[[s, emps]])\n\n")
+        .returnsUnordered(
+            "empid=100",
+            "empid=110",
+            "empid=150",
+            "empid=200");
+  }
+
   /** Test case for
    * <a href="https://issues.apache.org/jira/browse/CALCITE-2920">[CALCITE-2920]
    * RelBuilder: new method to create an anti-join</a>. */