# Query Execution > 这个 project 主要是实现增加对数据库系统的执行计划的支持。需要实现各种 **executors**，将 **query plan** 传入 executors 然后执行它们。需要实现下列的 executors： > > * **Access Methods:** Sequential Scans, Index Scans > * **Modifications:** Inserts, Updates, Deletes > * **Miscellaneous:** Nested Loop Joins, Index Nested Loop Joins, Aggregation, Limit/Offset 我们需要实现迭代查询处理模型，每个查询计划执行器实现了一个 `Init()` 函数和 `Next()` 函数。当 DBMS 调用 executors 的 `Next()` 函数时，它会返回 * 一个 `tuple` 并返回 `true` * 没有 `tuple` 可以再返回时，返回 `false` ### TASK #1 - SYSTEM CATALOG > 这个 task 不难，主要是实现 `src/include/catalog/catalog.h` 文件（catalog 维护了数据库的 meta-data）中的要求实现的函数，这些函数与数据库的表和索引有关。 * `GetTable()` 使用 `std::unordered_map` 的 `at` 函数，它会做下标检查，当 `key` 不存在时会抛出异常 * 在 `CreateIndex` 函数中，创建表的索引时，需要使用 table heap 的迭代器取出每个 tuple，然后使用 tuple 的 `KeyFromTuple` 构造 **key tuple** 插入到 B+ Tree 中 *** ### TASK #2 - EXECUTORS #### SEQUENTIAL SCAN > 在顺序执行器中，如何保存 `table_heap_` 的迭代器呢？一直没找到解决方案，因为我先选择在使用 `std::vector` 先保存结果，然后在 `Next` 中一个一个返回。在返回结果时，记得要根据 `OutputSchema` 构造 tuple 返回 | 
Tuple make_tuple(const Tuple &tuple, const Schema *output_schema) {
std::vector<Value> values;
for (const auto &col : output_schema->GetColumns()) {
values.push_back(tuple.GetValue(output_schema, output_schema->GetColIdx(col.GetName())));
}
return Tuple(values, output_schema);
}







INDEX SCANS

通过 B+ Tree 索引，先获得 RID，然后根据 RID 在 table_heap_ 中得到对应的 tuple


通过 dynamic_cast<BPlusTreeIndex<GenericKey<8>, RID, GenericComparator<8>> *>(indexInfo_->index_.get()); 将 Index 转成 BPlusTreeIndex 类型

INSERT


插入执行器需要区分待插入的数据是 RawInsert 还是来自 child_executor_
如果待插入的表存在索引需要使用 KeyFromTuple 构造 index_key，然后将它插入到 B+ Tree 索引中
engine 在插入、更新、删除不需要将 tuple 添加到 result_set 中，否则在 test 中会报 result_set 不为空的错误


UPDATE

由 child_executor_ 的 Next 提供 tuple，然后调用 GenerateUpdatedTuple 生成待更新的 tuple，最后使用 table_heap_->UpdateTuple 进行更新操作

DELETE


由 child_executor_ 的 Next 提供 tuple
调用 table_heap_->MarkDelete 标记这个 tuple 需要删除
如果待插入的表存在索引需要使用 KeyFromTuple 构造 index_key，然后在 B+ Tree 索引中将这个 Key 删除


NESTED LOOP JOIN

使用 left_executor 和 right_executor 提供的 tuple 进行 EvaluateJoin 构造符合条件的 tuple

INDEX NESTED LOOP JOIN

使用索引来进行 Join，这样就不需要扫描整个 inner table。因此我们需要将 outer tuple 转化为对应的 key，然后在 inner table index 中进行查找。


测试/验证/打包

测试

cd buildmake executor_test

格式验证

make formatmake check-lintmake check-clang-tidy

打包

zip project3-submission.zip src/include/buffer/lru_replacer.h src/buffer/lru_replacer.cpp \	src/include/buffer/buffer_pool_manager.h src/buffer/buffer_pool_manager.cpp \	src/include/storage/page/b_plus_tree_page.h src/storage/page/b_plus_tree_page.cpp \	src/include/storage/page/b_plus_tree_internal_page.h src/storage/page/b_plus_tree_internal_page.cpp \	src/include/storage/page/b_plus_tree_leaf_page.h src/storage/page/b_plus_tree_leaf_page.cpp \	src/include/storage/index/b_plus_tree.h src/storage/index/b_plus_tree.cpp \	src/include/storage/index/index_iterator.h src/storage/index/index_iterator.cpp \	src/include/catalog/catalog.h src/include/execution/execution_engine.h src/include/storage/index/index.h \	src/include/execution/executor_factory.h src/execution/executor_factory.cpp \	src/include/execution/executors/seq_scan_executor.h src/execution/seq_scan_executor.cpp \	src/include/execution/executors/index_scan_executor.h src/execution/index_scan_executor.cpp \	src/include/execution/executors/insert_executor.h src/execution/insert_executor.cpp \	src/include/execution/executors/update_executor.h src/execution/update_executor.cpp \	src/include/execution/executors/delete_executor.h src/execution/delete_executor.cpp \	src/include/execution/executors/nested_loop_join_executor.h src/execution/nested_loop_join_executor.cpp \	src/include/execution/executors/nested_index_join_executor.h src/execution/nested_index_join_executor.cpp \	src/include/execution/executors/limit_executor.h src/execution/limit_executor.cpp \	src/include/execution/executors/aggregation_executor.h src/execution/aggregation_executor.cpp \	src/include/storage/index/b_plus_tree_index.h src/storage/index/b_plus_tree_index.cpp
然后前往  提交代码
--- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://rookiedong.gitbook.io/notes/databases/cmu-15-445/query-execution.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.