mysql运算符和常用函数+自定义函数
在本文将总结概括mysql的运算符和常用函数，自定义函数
常用函数
- 字符函数
- 数值运算符函数
- 比较运算符和函数
- 日期时间函数
- 信息函数
- 聚合函数（用于数据表中）
- 加密函数
1. 字符函数
| 函数名 | 解释 |
|---|---|
| CONCAT() | 字符连接 |
| CONCAT_WS() | 使用制定的分隔符进行字符连接 |
| FORMAT() | 数字格式化 |
| LOWER() | 转换未小写字母 |
| UPPER() | 转换成大写字母 |
| LEFT() | 获取左侧字符 |
| RIGHT() | 获取右侧字符 |
| LENGTH() | 获取字符串长度 |
| LTRIM() | 删除前导空格 |
| RTRIM() | 删除后导和后续空格 |
| SUBSTRING() | 字符串截取 |
| [NOT]LIKE | 模式匹配（%任意个字符，_任意一个字符） |
| REPLACE() | 字符串替换 |
CONCAT()
mysql> select concat('imooc','mysql');
+-------------------------+
| concat('imooc','mysql') |
+-------------------------+
| imoocmysql |
+-------------------------+
1 row in set (0.04 sec)
mysql> select concat('imooc','-','mysql');
+-----------------------------+
| concat('imooc','-','mysql') |
+-----------------------------+
| imooc-mysql |
+-----------------------------+
1 row in set (0.00 sec)
mysql> select concat_ws('-','imooc','51cto','bei');
+--------------------------------------+
| concat_ws('-','imooc','51cto','bei') |
+--------------------------------------+
| imooc-51cto-bei |
+--------------------------------------+
1 row in set (0.00 sec)
mysql> select lower('MYSQL');
+----------------+
| lower('MYSQL') |
+----------------+
| mysql |
+----------------+
1 row in set (0.00 sec)
mysql> select upper('mysQl');
+----------------+
| upper('mysQl') |
+----------------+
| MYSQL |
+----------------+
1 row in set (0.00 sec)
mysql> select left('mysql',3);
+-----------------+
| left('mysql',3) |
+-----------------+
| mys |
+-----------------+
1 row in set (0.00 sec)
mysql> select lower(left('MYSQL',2));
+------------------------+
| lower(left('MYSQL',2)) |
+------------------------+
| my |
+------------------------+
1 row in set (0.00 sec)
mysql> select right('mysql',1);
+------------------+
| right('mysql',1) |
+------------------+
| l |
+------------------+
1 row in set (0.00 sec)
mysql> select length('mysql');
+-----------------+
| length('mysql') |
+-----------------+
| 5 |
+-----------------+
1 row in set (0.03 sec)
mysql> select ltrim(' mysql ');
+---------------------+
| ltrim(' mysql ') |
+---------------------+
| mysql |
+---------------------+
1 row in set (0.00 sec)
mysql> select ltrim(' mysql b ');
+-----------------------+
| ltrim(' mysql b ') |
+-----------------------+
| mysql b |
+-----------------------+
1 row in set (0.00 sec)
mysql> select length(ltrim(' mysql '));
+-----------------------------+
| length(ltrim(' mysql ')) |
+-----------------------------+
| 8 |
+-----------------------------+
1 row in set (0.00 sec)
mysql> select length(rtrim(' mysql '));
+-----------------------------+
| length(rtrim(' mysql ')) |
+-----------------------------+
| 7 |
+-----------------------------+
1 row in set (0.00 sec)
mysql> select trim(leading '?' from '???mysql???');
+--------------------------------------+
| trim(leading '?' from '???mysql???') |
+--------------------------------------+
| mysql??? |
+--------------------------------------+
1 row in set (0.00 sec)
mysql> select trim(trailing '?' from '???mysql???');
+---------------------------------------+
| trim(trailing '?' from '???mysql???') |
+---------------------------------------+
| ???mysql |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select trim(both '?' from '???mysql???');
+-----------------------------------+
| trim(both '?' from '???mysql???') |
+-----------------------------------+
| mysql |
+-----------------------------------+
1 row in set (0.00 sec)
mysql> select trim(both '?' from '???my??sql???');
+-------------------------------------+
| trim(both '?' from '???my??sql???') |
+-------------------------------------+
| my??sql |
+-------------------------------------+
1 row in set (0.00 sec)
mysql> select replace('??mysql??sql??','?','');
+----------------------------------+
| replace('??mysql??sql??','?','') |
+----------------------------------+
| mysqlsql |
+----------------------------------+
1 row in set (0.00 sec)
mysql> select replace('??mysql??sql??','?','2');
+-----------------------------------+
| replace('??mysql??sql??','?','2') |
+-----------------------------------+
| 22mysql22sql22 |
+-----------------------------------+
1 row in set (0.00 sec)
mysql> select replace('??mysql??sql??','??','2');
+------------------------------------+
| replace('??mysql??sql??','??','2') |
+------------------------------------+
| 2mysql2sql2 |
+------------------------------------+
1 row in set (0.00 sec)
mysql> select substring('mysql',1,2);
+------------------------+
| substring('mysql',1,2) |
+------------------------+
| my |
+------------------------+
1 row in set (0.00 sec)
mysql> select substring('mysql',3);
+----------------------+
| substring('mysql',3) |
+----------------------+
| sql |
+----------------------+
1 row in set (0.00 sec)
mysql> select substring('mysql',-1);
+-----------------------+
| substring('mysql',-1) |
+-----------------------+
| l |
+-----------------------+
1 row in set (0.02 sec)
mysql> select substring('mysql',-3,2);
+-------------------------+
| substring('mysql',-3,2) |
+-------------------------+
| sq |
+-------------------------+
2. 数值运算符函数
| 函数名 | 解释 |
|---|---|
| CEIL() | 进一取整 |
| DIV | 整数除法 |
| FLOOR() | 舍一取整 |
| MOD | 取余数（取模） |
| POWER() | 幂运算 |
| ROUND() | 四舍五入 |
| TRUNCATE() | 数字截取 |
mysql> select ceil(3.01);
+------------+
| ceil(3.01) |
+------------+
| 4 |
+------------+
1 row in set (0.04 sec)
mysql> select floor(3.9999);
+---------------+
| floor(3.9999) |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)
mysql> select 3/4;
+--------+
| 3/4 |
+--------+
| 0.7500 |
+--------+
1 row in set (0.00 sec)
mysql> select 3 div 4;
+---------+
| 3 div 4 |
+---------+
| 0 |
+---------+
1 row in set (0.00 sec)
mysql> select 5%3;
+------+
| 5%3 |
+------+
| 2 |
+------+
1 row in set (0.00 sec)
mysql> select 5 mod 3;
+---------+
| 5 mod 3 |
+---------+
| 2 |
+---------+
1 row in set (0.00 sec)
mysql> select power(2,3);
+------------+
| power(2,3) |
+------------+
| 8 |
+------------+
1 row in set (0.05 sec)
mysql> select round(3.5554,2);
+-----------------+
| round(3.5554,2) |
+-----------------+
| 3.56 |
+-----------------+
1 row in set (0.00 sec)
mysql> select round(4.544,0);
+----------------+
| round(4.544,0) |
+----------------+
| 5 |
+----------------+
1 row in set (0.00 sec)
mysql> select truncate(125.89,2);
+--------------------+
| truncate(125.89,2) |
+--------------------+
| 125.89 |
+--------------------+
1 row in set (0.00 sec)
mysql> select truncate(125.89,1);
+--------------------+
| truncate(125.89,1) |
+--------------------+
| 125.8 |
+--------------------+
1 row in set (0.00 sec)
mysql> select truncate(125.89,0);
+--------------------+
| truncate(125.89,0) |
+--------------------+
| 125 |
+--------------------+
1 row in set (0.00 sec)3. 比较运算符和函数
| 函数名 | 解释 |
|---|---|
| [NOT] BETWEEN…AND… | [不]在范围之内 |
| [NOT] IN() | [不]在列出值范围内 |
| IS [NOT] NULL | [不]为空 |
mysql> select 15 between 1 and 22;
+---------------------+
| 15 between 1 and 22 |
+---------------------+
| 1 |
+---------------------+
1 row in set (0.00 sec)
mysql> select 35 between 1 and 22;
+---------------------+
| 35 between 1 and 22 |
+---------------------+
| 0 |
+---------------------+
1 row in set (0.00 sec)
mysql> select 35 not between 1 and 22;
+-------------------------+
| 35 not between 1 and 22 |
+-------------------------+
| 1 |
+-------------------------+
1 row in set (0.00 sec)
mysql> select 10 in (15,10,12);
+------------------+
| 10 in (15,10,12) |
+------------------+
| 1 |
+------------------+
1 row in set (0.00 sec)
mysql> select 100 in (15,10,12);
+-------------------+
| 100 in (15,10,12) |
+-------------------+
| 0 |
+-------------------+
1 row in set (0.00 sec)
mysql> select 100 not in (15,10,12);
+-----------------------+
| 100 not in (15,10,12) |
+-----------------------+
| 1 |
+-----------------------+
1 row in set (0.00 sec)4. 日期时间函数
| 函数名 | 解释 |
|---|---|
| NOW() | 当前日期和时间 |
| CURDATE() | 当前日期 |
| CURTIME() | 当前时间 |
| DATE_ADD() | 日期变化 |
| DATEDIFF() | 日期差值 |
| DATE_FORMAT() | 日期格式化 |
mysql> select now();
+---------------------+
| now() |
+---------------------+
| 2017-04-27 20:52:45 |
+---------------------+
1 row in set (0.07 sec)
mysql> select curdate();
+------------+
| curdate() |
+------------+
| 2017-04-27 |
+------------+
1 row in set (0.03 sec)
mysql> select curtime();
+-----------+
| curtime() |
+-----------+
| 20:53:13 |
+-----------+
1 row in set (0.00 sec)
mysql> select date_add('2014-3-12',interval 365 day);
+----------------------------------------+
| date_add('2014-3-12',interval 365 day) |
+----------------------------------------+
| 2015-03-12 |
+----------------------------------------+
1 row in set (0.03 sec)
mysql> select date_add('2014-3-12',interval 5 week);
+---------------------------------------+
| date_add('2014-3-12',interval 5 week) |
+---------------------------------------+
| 2014-04-16 |
+---------------------------------------+
1 row in set (0.00 sec)
mysql> select datediff('2013-3-12','2014-5-12');
+-----------------------------------+
| datediff('2013-3-12','2014-5-12') |
+-----------------------------------+
| -426 |
+-----------------------------------+
1 row in set (0.03 sec)
mysql> select date_format('2017-3-12','%m/%d/%Y');
+-------------------------------------+
| date_format('2017-3-12','%m/%d/%Y') |
+-------------------------------------+
| 03/12/2017 |
+-------------------------------------+
1 row in set (0.00 sec)5. 信息函数
| 函数名 | 解释 |
|---|---|
| CONNECTION_ID() | 连接ID |
| DATABASE() | 当前数据库名称 |
| LAST_INSERT_ID() | 最后插入记录的ID号 |
| USER() | 当前用户 |
| VERSION() | 版本信息 |
6. 聚合函数（用于数据表中）
| 函数名 | 解释 |
|---|---|
| AVG() | 平均值 |
| COUNT() | 计数 |
| MAX() | 最大值 |
| MIN() | 最小值 |
| SUM() | 求和 |
7. 加密函数
| 函数名 | 解释 |
|---|---|
| MD5() | 信息摘要算法 |
| PASSWORD() | 密码算法 |
自定义函数
CREATE [AGGREGATE] FUNCTION function_name(parameter_name type,[parameter_name type,...])
RETURNS {STRING|INTEGER|REAL}
runtime_body自定义函数的两个必要条件
1）参数（最多可以有1024个，实际开发中不需要那么多）
2）返回值（所有的函数都有返回值，包括自定义函数，返回值可以是任意类型的值）
关于函数体
1）函数体由合法的SQL语句构成；
2）函数体可以是简单的SELECT或INSERT语句；
3）函数体如果为复合结构则使用BEGIN…END语句；
4）复合结构可以包含声明，循环，控制结构
删除函数
DROP FUNCTION [IF EXISTS] function_name一、创建一个不带参数的自定义函数
mysql> create function f1() returns varchar(30)
-> return date_format(now(),'%Y年%m月%d日 %H点:%i分:%s秒');
Query OK, 0 rows affected (0.08 sec)
mysql> select f1();
+-------------------------------+
| f1() |
+-------------------------------+
| 2017年04月27日 21点:35分:47秒 |
+-------------------------------+
1 row in set (0.03 sec)二、创建带参数的自定义函数
mysql> create function f2(num1 smallint unsigned,num2 smallint unsigned)
-> returns float(10,2) unsigned
-> return (num1+num2)/2;
Query OK, 0 rows affected (0.02 sec)
mysql> select f2(2,3);
+---------+
| f2(2,3) |
+---------+
| 2.50 |
+---------+
1 row in set (0.02 sec)三、创建具有复合结构函数体的自定义函数
mysql> create function addArticle(a_title varchar(20),a_content varchar(20),a_uid tinyint(1))
-> returns int unsigned
-> BEGIN
-> insert article (title,content,uid) values (a_title,a_content,a_uid);
-> return last_insert_id();
-> END
-> //
Query OK, 0 rows affected (0.03 sec)
mysql> select addArticle('标题','内容','3');
+-------------------------------+
| addArticle('标题','内容','3') |
+-------------------------------+
| 5 |
+-------------------------------+
1 row in set (0.08 sec)