Mysql生成随机字符串，大小写转换和固定长度
1、生成随机字符串，长度是1-20
select substring(MD5(RAND()),1,20) 2、生成随机字符串 长度是1-20，要求大写 select UPPER(substring(MD5(RAND()),1,5)) 3、生成随机字符串 长度是1-20，要求小写 select LCASE(substring(MD5(RAND()),1,5))
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select substring(MD5(RAND()),1,20) 2、生成随机字符串 长度是1-20，要求大写 select UPPER(substring(MD5(RAND()),1,5)) 3、生成随机字符串 长度是1-20，要求小写 select LCASE(substring(MD5(RAND()),1,5))