fix(p3): nlj check should only consider number of actual tuples (#556)

* fix(p3): nlj check should only consider number of actual tuples

Signed-off-by: Alex Chi <[email protected]>

* fix

Signed-off-by: Alex Chi <[email protected]>

---------

Signed-off-by: Alex Chi <[email protected]>

Author: skyzh

src/execution/init_check_executor.cpp

@@ -29,13 +29,12 @@ void InitCheckExecutor::Init() {
 }
 
 auto InitCheckExecutor::Next(Tuple *tuple, RID *rid) -> bool {
-  if (!child_executor_) {
-    return EXECUTOR_EXHAUSTED;
-  }
-
   // Emit the next tuple
-  n_next_++;
-  return child_executor_->Next(tuple, rid);
+  auto result = child_executor_->Next(tuple, rid);
+  if (result) {
+    n_next_++;
+  }
+  return result;
 }
 
 }  // namespace bustub

src/include/execution/execution_engine.h

@@ -79,8 +79,9 @@ class ExecutionEngine {
     for (const auto &[left_executor, right_executor] : exec_ctx->GetNLJCheckExecutorSet()) {
       auto casted_left_executor = dynamic_cast<const InitCheckExecutor *>(left_executor);
       auto casted_right_executor = dynamic_cast<const InitCheckExecutor *>(right_executor);
-      BUSTUB_ASSERT(casted_left_executor->GetNextCount() == casted_right_executor->GetInitCount(),
-                    "nlj check failed, are you initialising the right executor correctly?");
+      BUSTUB_ASSERT(casted_right_executor->GetInitCount() + 1 >= casted_left_executor->GetNextCount(),
+                    "nlj check failed, are you initialising the right executor every time when there is a left tuple? "
+                    "(off-by-one is okay)");
     }
   }