MySQL - 替换，大小写，拼接，取几位，长度

//长度
length(catName)
//取第一位字符
substring(catName,1,1)
//转大写
upper(substring(catName,1,1))
//转小写
lower(substring(catName,1,length(catName)))
//拼接concat("","",""),前两个参数是需要拼接的字符串，最后一个为以什么拼接比如：
mysql> concat("a","b","===")
mysql> a===b
concat(upper(substring(catName,1,1)),lower(substring(catName,1,length(catName))),"")

mysql> select concat(upper(substring(catName,1,1)),lower(substring(catName,1,length(catName))),"") from cat;

//把a替换成A
mysql> select replace(catName,'a','A') from cat;