[大数据]MySQL不要用utf8编码而要用utf8mb4编码

MySQL的utf8mb4, mb4全称most 4 bytes, 最大4字节，才能支持真正的utf8所有字符。

排序要用utf8mb4对应的排序规则，一般为utf8mb4_general_ci。

官方文档原文内容为：

The utfmb4 character set has these characteristics:

• Supports BMP and supplementary characters.

• Requires a maximum of four bytes per multibyte character.