语法：
select 字段...
from
表名
where ... 筛选条件
筛选条件分类：
1 简单运算符
= != < > <= >=
2逻辑运算符
or
and
not
3模糊查询
like
betton and
in
is null is not null
条件查询
原文：https://www.cnblogs.com/jiaowoxiaofeng/p/12198822.html
