[Aleknagik]

用在SELECT语句，以及子句 where, order by, having中的UPDATE, DELETE

mysql>select 1+1;
mysql>select concat("abc","xyz");
mysql>select concat("abc","opq","uvw","zzz");

函数中可以将字段名作为变量来用，变更的值就是这个列对应的每一行记录
select 语句，对于表来说，列就是变量
如表users中有name, age两个字段
mysql>select concat(name," age is ",age)from users;
一、字符串函数
CONCAT(S1,S2,...Sn) 把传入的参数连接成一个字符串
INSERT(str,x,y,insert) 将字符串x位置开始，y个字符串长度替换为字符串insert
mysql>select insert("abcdefg",2,3,"hello");
mysql>select insert(name,3,2,'00' from users;
mysql>select insert(name,3,2,'00', name from users;

LOWER(str) 将传入的字符串变成小写
UPPER(str) 将传入的字符串变成大写
mysql>select lower("HELLOW"),upper('hello");
mysql>select * from users where upper(name)='AAA';

LEFT（str,x) 返回字符串最左边的x个字符
RIGHTstr,x) 返回字符串最右边的x个字符
mysql>select left("abcdefg",3),right("abcdefg",3);
二、数值函数
三、日期函数