1、replace 函数

语法：replace(object,search,replace)
含义：把object中出现search的全部替换为replace

select replace('张  三',' ','');
+---------------------------+  
| replace('张  三',' ','')   |  
+---------------------------+ 
| 张三                       |  
+---------------------------+ 

--把表table中的name字段中的空格去掉 
update table set name=replace(name,' ','') 

2、trim 函数

语法：trim([{BOTH | LEADING | TRAILING} [remstr] FROM] str)
含义：去掉字符串前面或后面指定的字符串

--1、去掉字符串前后的空格
SELECT TRIM(' zhangsan  ');
+---------------------------+  
| TRIM(' zhangsan  ')       |  
+---------------------------+ 
| zhangsan                  |  
+---------------------------+ 
--2、去掉左边指定的字符串
SELECT TRIM(LEADING 'x' FROM 'xxxzhangsanxxx');
+------------------------------------------------+  
| TRIM(LEADING 'x' FROM 'xxxzhangsanxxx')        |  
+------------------------------------------------+ 
| zhangsanxxx                                    |  
+------------------------------------------------+ 
--3、去掉右边指定的字符串
SELECT TRIM(TRAILING 'x' FROM 'xxxzhangsanxxx');
+------------------------------------------------+  
| TRIM(TRAILING 'x' FROM 'xxxzhangsanxxx')       |  
+------------------------------------------------+ 
| xxxzhangsan                                    |  
+------------------------------------------------+ 
--4、去掉前后指定的字符串
SELECT TRIM(BOTH 'x' FROM 'xxxzhangsanxxx');
+------------------------------------------------+  
| TRIM(BOTH 'x' FROM 'xxxzhangsanxxx')           |  
+------------------------------------------------+ 
| zhangsan                                       |  
+------------------------------------------------+