# 时间操作函数selectNOW();# 整体获取当前日期以及时间selectCURDATE();# 获取年月日selectCURTIME();# 获取时分秒# 获取单个年月日时分秒信息selectYEAR(2022-02-02 22:22:22);selectYEAR(NOW())年份,MONTH(NOW())月份,DAY(NOW())日期,HOUR(NOW())小时,MINUTE(NOW())分钟,SECOND(NOW())秒数;# 计算时间差·单位是天数-1selectDATEDIFF(2022-02-02 22:22:22,NOW())相差时间;# 日期相加selectADDDATE(2020-02-02 22:22:22,28);#字符串函数selectCONCAT(H,e,1,1,o,.)#将数据库中的查询的信息进行新组合selectCONCAT(country:,name)as国家名称fromcountrywhereCodeAND;#英文大小写转换selectLOWER(name)国家名称-小写 UPPER(name)国家名称-大写fromcountry wherCodeAND;# 字符串的截取·从下标开始截取个数selectSUBSTRING(我拥有一个美丽的梦想,6,5)as修饰词;# 替换selectREPLACE(你是个大马猴你的朋友也是大马猴,大马猴,***);select6.01as操作数,CEIL(6.01)向上取整,FLOOR(6.01)向下取整;select6.99as操作数,CEIL(6.99)向上取整,FLOOR(6.99)向下取整;select6.00as操作数,CEIL(6.00)向上取整,FLOOR(6.00)向下取整;selectRAND();# 返回0~1的一个随机数selectfloor(RAND()*10)转换成字符1,floor(RAND()*10)转换成字符2,floor(RAND()*10)转换成字符3,floor(RAND()*10)转换成字符4,floor(RAND()*10)转换成字符5,floor(RAND()*10)转换成字符6;