MySql学习记录4-字符串处理函数

常用的字符串处理函数有：

Length(str) － 求字符串长度
Ltrim(str) － 去掉左边的空格
Rtrim(str) － 去掉右边的空格
Left(str,n); － 从左边取出n个字符
Right(str,n); － 从右边取出n个字符
Substring(str,begin,len) －返回子串, begin的序号从1开始
Reverse(str) –返回颠倒的字符串
Lower(str) － 转成小写
Upper(str) － 转成大写
Concat(Str,str…..)串联字符串。
Instr(str,s) – 返回s在str中出面的位置，没有则返回0

1.Length(str)--返回str

SELECT address FROM stud WHERE LENGTH(address)>3;

2.Ltrim(str),Rtrim(str),trim(str)--分别是去掉左边,右边,两边的空格

SELECT TRIM(address) AS address FROM stud;
SELECT LTRIM(address) AS address FROM stud;
SELECT RTRIM(address) AS address FROM stud;

3.Left(str,n),Right(str,n)--分别是从左边,右边取出n个字符

SELECT LEFT(address,2) AS address FROM stud;
SELECT RIGHT(address,2) AS address FROM stud;

4. Substring(str,begin,len) －返回子串, begin的序号从1开始

SELECT SUBSTRING(address,2,2) AS address FROM stud;

5. Reverse(str) –返回颠倒的字符串

SELECT REVERSE(address) AS address FROM stud;

6. Lower(str)、Upper(str):转换为小写、大写

SELECT LOWER(address) AS address FROM stud;
SELECT UPPER(address) AS address FROM stud;

7. Concat(Str,str…..)串联字符串。

SELECT CONCAT(sname,address) AS 'name+address' FROM stud;

8. Instr(str,s) – 返回s在str中出面的位置，没有则返回0

SELECT INSTR(address,'湖南') AS 位置 FROM stud;