调整文档格式&编译警告 (#85)

* fix -Wunused-function

* 调整文档格式

docs/how_to_dev_miniob_by_vscode.md

@@ -24,11 +24,10 @@ UBUNTU_CODENAME=focal
 2. cmake
 3. make
 4. gcc/g++
-
-3. libevent
-5. googletest
-6. jsoncpp
-7. git
+5. libevent
+6. googletest
+7. jsoncpp
+8. git
 
 ## 获取代码
 ```bash

src/observer/net/server.cpp

@@ -189,7 +189,6 @@ int Server::send(ConnectionContext *client, const char *buf, int data_len)
   TimerStat writeStat(*write_socket_metric_);
 
   MUTEX_LOCK(&client->mutex);
-  int wlen = 0;
   int ret = common::writen(client->fd, buf, data_len);
   if (ret < 0) {
     LOG_ERROR("Failed to send data back to client. ret=%d, error=%s", ret, strerror(errno));

src/observer/sql/stmt/select_stmt.cpp

@@ -46,7 +46,7 @@ RC SelectStmt::create(Db *db, const Selects &select_sql, Stmt *&stmt)
   // collect tables in `from` statement
   std::vector<Table *> tables;
   std::unordered_map<std::string, Table *> table_map;
-  for (int i = 0; i < select_sql.relation_num; i++) {
+  for (size_t i = 0; i < select_sql.relation_num; i++) {
     const char *table_name = select_sql.relations[i];
     if (nullptr == table_name) {
       LOG_WARN("invalid argument. relation name is null. index=%d", i);