第 4 章 傅里叶级数的一些应用
Fourier series and analogous expansions intervene very
naturally in the general theory of curves and surfaces.
In effect, this theory, conceived from the point of view
of analysis, deals obviously with the study of arbitra…
rand()函数:随机返回0-1之间的小数
floor()函数:小数向下取证书。向上取整数ceiling()
concat_ws函数:将括号内数据用第一个字段连接起来
group by子句:分组语句,常用语结合统计函数,根据一个或多个列&a…