说明：  本课程主要介绍了高级子查询及SQL开发中级一测试知识。其中高级子查询主要包括单列子查询、多列子查询、相关子查询、Exists操作符、相关更新/删除、with子句。语言通俗易懂，概念清晰、深入浅出，易于学习。
(This course mainly introduces the advanced sub query and the middle level test knowledge of SQL development. One senior sub query includes single query, multi query, Liezi Liezi related sub query, Exists operator, update / delete, with clause. The language is easy to understand, clear concept, easy to understand, easy to learn.)