mysql 内置函数的
- 慎用，慎用，慎用
字符串
select 的主要功能其实是打印
1
concat() 拼接字符串
select concat("我","你") as 拼接;
+------+
| 拼接 |
+------+
| 我你 |
+------+
2
length(str) 获取字符串长度
select length("夜晚有多长") as 今夜;
+------+
| 今夜 |
+------+
| 10 |
+------+
3
lower(str)所有字符串小写
select lower("TO THE MOON") as for_river ;
+-------------+
| for_river |
+-------------+
| to the moon |
+-------------+
4
upper(str)所有字符串大写
select upper("little dog") as 星座;
+------------+
| 星座 |
+------------+
| LITTLE DOG |
+------------+
5
left(str,x) 返回字符串str最左边的x个字符串
select left("涉江采芙蓉",2);
+----------------------+
| left("涉江采芙蓉",2) |
+----------------------+
| 涉江 |
+----------------------+
6
right（str,x）
select right("涉江采芙蓉",2);
+-----------------------+
| right("涉江采芙蓉",2) |
+-----------------------+
| 芙蓉 |
+-----------------------+
7
lpad(str,n,pad) 用字符串pad对str最右边填充直到长度为n
mysql> select lpad("你是谁",5,"谁");
+-----------------------+
| lpad("你是谁",5,"谁") |
+-----------------------+
| 谁谁你是谁 |
+-----------------------+
select rpad("你是谁",5,"谁");
+-----------------------+
| rpad("你是谁",5,"谁") |
+-----------------------+
| 你是谁谁谁 |
+-----------------------+
8
ltrim 去除最左边空格
mysql> select ltrim(' haha');
+-------------------------+
| ltrim(' haha') |
+-------------------------+
| haha |
+-------------------------+
1 row in set (0.00 sec)
9
right 去除右边空格
mysql> select concat(rtrim(' haha '),'world'); #去除右侧空格
+------------------------------------------------+
| concat(rtrim(' haha '),'world') |
+------------------------------------------------+
| hahaworld |
+------------------------------------------------+
10
trim() 去除两边空格
select trim(" fds ");
+--------------------+
| trim(" fds ") |
+--------------------+
| fds |
+--------------------+
11
repeat（str，x）返回字符串中出现x次的结果
12
replace （str，a,b）将字符串中的a替换成b
13
strcmp(s1,s2)
比较两个字符串 完全一样返回0 s1的首字母比s2的首字母大返回1 否则返回-1
14
mysql> select substr("python is so good",1,5); #从下标1开始截取5个
+---------------------------------+
| substr("python is so good",1,5) |
+---------------------------------+
| pytho |
+---------------------------------+
数学
1. bin() # 10进制转2进制
mysql> select bin(99);
+---------+
| bin(99) |
+---------+
| 1100011 |
+---------+
2. ceiling() # 向上取整
mysql> select ceiling(13.1);
+---------------+
| ceiling(13.1) |
+---------------+
| 14 |
+---------------+
3. floor() #向下取整
mysql> select floor(13.1);
+-------------+
| floor(13.1) |
+-------------+
| 13 |
+-------------+
4. max()
5. min()
6. sqrt()
mysql> select sqrt(10);
+--------------------+
| sqrt(10) |
+--------------------+
| 3.1622776601683795 |
+--------------------+
7. rand()
mysql> select rand();
+--------------------+
| rand() |
+--------------------+
| 0.3009522643880474 |
+--------------------+
日期
1
now() #当前的日期加时间
2
year(date) # date日期坐在的年份
3
month(date) # date日期坐在的月份
4
week(date) # date日期坐在的第几周
5
unix_timestamp(date) #日期所在的时间戳
6
from_unixtime(时间戳) #时间戳转日期
7
mysql> select datediff('1998-10-20','2015-7-23'); #日期差额