fix: wrong index in cell_at() of JoinTuple and redundant species when…

… calling open() repeatedly (#16)

bug 1:  join tuple cannot be visited by cell_at() at position 0
bug 2: row tuple's schema will be double or triple initialized when
trying to reopen table scanner

src/server/include/query_engine/structor/tuple/join_tuple.h

@@ -44,7 +44,7 @@ class JoinedTuple : public Tuple
   RC cell_at(int index, Value &value) const override
   {
     const int left_cell_num = left_->cell_num();
-    if (index > 0 && index < left_cell_num) {
+    if (index >= 0 && index < left_cell_num) {
       return left_->cell_at(index, value);
     }
 
@@ -68,4 +68,4 @@ class JoinedTuple : public Tuple
 private:
   Tuple *left_ = nullptr;
   Tuple *right_ = nullptr;
-};
+};

src/server/include/query_engine/structor/tuple/row_tuple.h

@@ -8,10 +8,7 @@ class RowTuple : public Tuple
  RowTuple() = default;
  virtual ~RowTuple()
  {
-   for (FieldExpr *spec : species_) {
-     delete spec;
-   }
-   species_.clear();
+   _clear_species();
  }
 
  const TupleType tuple_type() const override { return RowTuple_Type; }
@@ -36,11 +33,22 @@ class RowTuple : public Tuple
    this->bitmap_.init(record->data() + null_filed_meta->offset(), null_filed_meta->len());
  }
 
+void _clear_species(){
+   if(!species_.empty()){
+    for(auto& field_expr : species_){
+      delete field_expr;  //clear()前先释放目前的fields
+    }
+    species_.clear();
+   }
+}
+
+
  void set_schema(const Table *table, const std::string &table_alias, const std::vector<FieldMeta> *fields)
  {
    table_ = table;
    table_alias_ = table_alias;
    this->species_.reserve(fields->size());
+   _clear_species(); //reopen时防止sepcies_就会积累多套重复的fields。
    for (const FieldMeta &field : *fields) {
      species_.push_back(new FieldExpr(table, &field));
      species_[species_.size() - 1]->set_field_table_alias(table_alias);