mysql bse什么意思_mysql 的几个理解

我看一个 sql 数据库文件，如下

DROP DATABASE IF EXISTS employees;

CREATE DATABASE IF NOT EXISTS employees;

USE employees;

SELECT 'CREATING DATABASE STRUCTURE' as 'INFO';

DROP TABLE IF EXISTS dept_emp,

dept_manager,

titles,

salaries,

employees,

departments;

set storage_engine = InnoDB;

-- set storage_engine = MyISAM;

-- set storage_engine = Falcon;

-- set storage_engine = PBXT;

-- set storage_engine = Maria;

select CONCAT('storage engine: ', @@storage_engine) as INFO;

有两个问题

1 这里的

SELECT 'CREATING DATABASE STRUCTURE' as 'INFO';

和 select CONCAT('storage engine: ', @@storage_engine) as INFO;

是个什么语法？是定义变量 INFO ？

为何一个有''一个没有引号？

2 这个 DROP TABLE 语句什么意思啊？ drop 哪个 table ？