单个临时表语法格式：with tmp as (select * from tb_name)
多个临时表的语法：
with
tmp as (select * from tb_name),
tmp2 as (select * from tb_name2),
tmp3 as (select * from tb_name3)
作用：
(1)SQL可读性增强，更有层次感。
(2)with子查询只执行一次，将结果存储在用户临时表空间中，可以引用多次，增强性能。
(3)将几个临时表建立关联
例子：
标签：name,临时,用法,语法,tb,select From： https://www.cnblogs.com/max1995/p/16709012.html