Mysql字符的使用

SELECT ASCII(user_password) as 阿斯克码 FROM users;#返回首字符的ascii码
SELECT CHAR_LENGTH(user_password) as 字符长度 FROM users;#返回字符长度
SELECT CHARACTER_LENGTH(user_password) as 字符长度 FROM users;#返回字符长度
SELECT CONCAT(id,user_password,class_id) as 拼接字符 from users;#返回拼接字符串
SELECT CONCAT_WS('_',id,user_password,class_id) as 拼接字符 from users;#返回带符号的拼接字符串
SELECT FIELD("杜甫",user_password) 查找的列 from users;#返回对应的位置
SELECT FIND_IN_SET("武则天",user_password) 查找对应字符 from users;#返回字符存在的位置

SELECT FORMAT(2000.54556,2) as 格式 ;#返回保留2位小数的字符
SELECT INSERT("baidu.com",1,5,"bing") as 改变链接;#返回第一位开始到第五位替换成新字符串bing的字符
SELECT LOCATE("武",user_password) as 位置 from users;#返回字符所在的位置，和find_in_set不同的是不需要完全匹配
SELECT POSITION("武" IN user_password) as 位置 from users;#返回字符所在的位置，和find_in_set不同的是不需要完全匹配,与locate相同
SELECT LCASE("Hallo World") AS 转换为小写;#返回转换为小写的字符

SELECT LEFT(user_password,1) As 首字符 from users;#返回1或n个长度的字符
SELECT LOWER("3DM") as 转换为小写;#转换为小写字符
SELECT LPAD("new",5,"real") as 拼接;#将real拼接到new前面直到变成5个字符，太长就删除多余字符
SELECT LTRIM("    李白") as 去除空格后;#去除左边的空白字符串
SELECT MID("两只老虎爱跳舞",3,5) as 截取;#截取第3个字符开始的五个字符同substring

SELECT REPEAT(user_password,3)as 自我拼接 from users;#字符串自我拼接3次
select REPLACE('好好学习，天天向上','学习','奋斗') as 替换;#把好好学习，天天向上的学习替换为奋斗
select REVERSE(user_password) as 翻转 from users;#反转字符串
SELECT RIGHT(user_password,2) as 后面两个字符 from users;#返回后面两个字符，和left相反
SELECT RPAD('happy',10,'new year') as 拼接字符;#把new year拼接到happy右边直到变成是个字符，多余的删除
SELECT RTRIM("李红     ") as 去除后面的空字符;#去除后面的空字符
SELECT CONCAT_WS(SPACE(10),id,user_password,class_id)  as 空字符拼接 from users;#space返回10个空字符
SELECT STRCMP('李世民','李二') as 返回值;#返回表达式大小，如：李世民<李二,所以返回-1；若李世民=李二，返回0；李世民大于李二，返回1
SELECT SUBSTR('happy',2,3) as 截取字段;#截取第二个字符开始3个字符和mid一样
SELECT substring('happy',2,3) as 截取字段;#截取第二个字符开始3个字符

SELECT UCASE("abcd") as 转换为大写;#返回大写
SELECT UPPER("chinese") as 转换为大写;#返回大写
SELECT TRIM("    李白    ") as 去掉前后的空格;#去除前后空格
SELECT SUBSTRING_INDEX("今晚打,老虎",",",1) as 截取;#以逗号为分割点，1返回左边的今晚打，-1返回老虎