logical plan & physical plan;
explain;
yacc rewrite;
join operator(nested loop join);
simple rewrite rules;
fix some issues of mysql protocol;

增加License、CODE_OF_CONDUCT、NOTICE和CONTRIBUTING文件
Co-authored-by: wangyunlai <hnwyllmm@126.com>

优化Docker开发环境：
- docker镜像使用zsh；
- 自动初始化vscode开发调试配置环境；
- 容器中开启ssh服务，方便远程开发；
- 可以在构建镜像时clone自己的代码；
- 提供了丰富详细的使用文档。

tested by mariadb ( Ver 15.1 Distrib 5.5.65-MariaDB, for Linux (x86_64) using readline 5.1)
but failed with obclient

如果使用readline，可以记录历史命令

* add comments for select-meta

Update problem specification for select-meta.

add cmake_prefix_path

add deps prefix

update googletest

update googletest

build googletest

2022 oceanbase competition

* 简化git submodule操作

* support build with address sanitizer

using cmake options `-DENALBE_ASAN=ON` to enable address sanitizer

* fix some memory leaks detected by asan

* fix -Wunused-function

* 调整文档格式