MySQL 内置函数

1. 日期函数

1.1 部分介绍

函数名	描述
CURRENT_DATE()	返回当前日期
CURRENT_TIME	返回当前时间
CURRENT_TIMESTAMP()	返回当前日期和时间
DATEDIFF(d1,d2)	计算日期 d1->d2 之间相隔的天数
DATE_ADD(d，INTERVAL expr type)	计算起始日期 d 加上一个时间段后的日期，type 值可以是： year, minute, second, hour, day, week…
DATE_SUB(date,INTERVAL expr type)	函数从日期减去指定的时间间隔。

这里仅列出了部分，详情见链接

1.2 获得当前日期，时间，时间戳，日期时间

mysql> select current_date();
+----------------+
| current_date() |
+----------------+
| 2024-11-24     |
+----------------+
1 row in set (0.07 sec)

mysql> select current_time();
+----------------+
| current_time() |
+----------------+
| 22:54:42       |
+----------------+
1 row in set (0.08 sec)

mysql> select current_timestamp();
+---------------------+
| current_timestamp() |
+---------------------+
| 2024-11-24 22:55:02 |
+---------------------+
1 row in set (0.07 sec)

mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2024-11-24 22:56:48 |
+---------------------+
1 row in set (0.10 sec)

1.2 返回`datetime`的日期部分

mysql> select date(now());
+-------------+
| date(now()) |
+-------------+
| 2024-11-24  |
+-------------+
1 row in set (0.10 sec)

mysql> select date(current_timestamp());
+---------------------------+
| date(current_timestamp()) |
+---------------------------+
| 2024-11-24                |
+---------------------------+
1 row in set (0.09 sec)

mysql> select date("2004-04-24 00:00:00");
+-----------------------------+
| date("2004-04-24 00:00:00") |
+-----------------------------+
| 2004-04-24                  |
+-----------------------------+
1 row in set (0.10 sec)

mysql> select date("2004-04-24 hhhxxxxxxxxxx");
+----------------------------------+
| date("2004-04-24 hhhxxxxxxxxxx") |
+----------------------------------+
| 2004-04-24                       |
+----------------------------------+
1 row in set (0.08 sec)

1.3 日期加减，日期的差

mysql> select date_add(current_date(), interval 1000 day);
+---------------------------------------------+
| date_add(current_date(), interval 1000 day) |
+---------------------------------------------+
| 2027-08-21                                  |
+---------------------------------------------+
1 row in set (0.09 sec)

mysql> select date_add(current_date(), interval 1000 year);
+----------------------------------------------+
| date_add(current_date(), interval 1000 year) |
+----------------------------------------------+
| 3024-11-24                                   |
+----------------------------------------------+
1 row in set (0.10 sec)

mysql> select date_sub(current_date(), interval 1000 month);
+-----------------------------------------------+
| date_sub(current_date(), interval 1000 month) |
+-----------------------------------------------+
| 1941-07-24                                    |
+-----------------------------------------------+
1 row in set (0.08 sec)

-- 拿前面的日期减后面的日期
mysql> select datediff(current_date(), '2004-04-25');
+----------------------------------------+
| datediff(current_date(), '2004-04-25') |
+----------------------------------------+
|                                   7518 |
+----------------------------------------+
1 row in set (0.11 sec)

mysql> select datediff('2004-04-25', current_date());
+----------------------------------------+
| datediff('2004-04-25', current_date()) |
+----------------------------------------+
|                                  -7518 |
+----------------------------------------+
1 row in set (0.09 sec)

1.4 示例1，创建一个留言板

创建留言板并插入数据

mysql> CREATE TABLE msg (id int PRIMARY KEY auto_increment, content VARCHAR(100), time DATETIME);

mysql> insert into msg (content, time) values("hello...", now());
Query OK, 1 row affected (0.03 sec)

mysql> insert into msg (content, time) values("world...", now());
Query OK, 1 row affected (0.03 sec)

mysql> select * from msg;
+----+----------+---------------------+
| id | content  | time                |
+----+----------+---------------------+
|  1 | hello... | 2024-11-25 20:33:09 |
|  2 | world... | 2024-11-25 20:33:18 |
+----+----------+---------------------+
2 rows in set (0.08 sec)

如果想查询10分钟内发布的帖子

mysql> select * from msg where date_add(time, interval 10 minute) > now();
+----+----------+---------------------+
| id | content  | time                |
+----+----------+---------------------+
|  1 | hello... | 2024-11-25 20:33:09 |
|  2 | world... | 2024-11-25 20:33:18 |
+----+----------+---------------------+
2 rows in set (0.09 sec)

mysql> select * from msg where date_sub(now(), interval 10 minute) < time;
+----+----------+---------------------+
| id | content  | time                |
+----+----------+---------------------+
|  1 | hello... | 2024-11-25 20:33:09 |
|  2 | world... | 2024-11-25 20:33:18 |
+----+----------+---------------------+
2 rows in set (0.10 sec)

2. 字符串函数

1.1 部分介绍

函数	描述
CONCAT(s1,s2…sn)	字符串 s1,s2 等多个字符串合并为一个字符串
INSTR(s1, s2)	返回s2在s1中的位置，没有返回0，类似strstr()
UCASE(s)	将字符串转换为大写
UPPER(s)	将字符串转换为大写
LEFT(s,n)	返回字符串 s 的前 n 个字符
RIGHT(s,n)	返回字符串 s 的后 n 个字符
LENGTH(s)	返回s字符串的长度，返回的是字节数
REPLACE(s,s1,s2)	将字符串 s2 替代字符串 s 中的字符串 s1
STRCMP(s1,s2)	比较字符串 s1 和 s2，如果 s1 与 s2 相等返回 0 ，如果 s1>s2 返回 1，如果 s1<s2 返回 -1
SUBSTR(s, start, length)	从字符串 s 的 start 位置截取长度为 length 的子字符串
LTRIM(s) RTRIM(s) TRIM(s)	去掉字符串 s 开始处的空格。去除s结尾处的空格。去除开头和结尾的空格
CHARSET(s)	返回字符串 s 的字符集

1.2 简单使用

-- concat
mysql> select concat("aaa", "bbbbb", 1234, "cd123");
+---------------------------------------+
| concat("aaa", "bbbbb", 1234, "cd123") |
+---------------------------------------+
| aaabbbbb1234cd123                     |
+---------------------------------------+
1 row in set (0.09 sec)

-- instr
mysql> select instr("aaaaaaabbbbbbcccccc", "aaa");
+-------------------------------------+
| instr("aaaaaaabbbbbbcccccc", "aaa") |
+-------------------------------------+
|                                   1 |
+-------------------------------------+
1 row in set (0.06 sec)

mysql> select instr("aaaaaaabbbbbbcccccc", "bbb");
+-------------------------------------+
| instr("aaaaaaabbbbbbcccccc", "bbb") |
+-------------------------------------+
|                                   8 |
+-------------------------------------+
1 row in set (0.07 sec)

mysql> select instr("aaaaaaabbbbbbcccccc", "f");
+-----------------------------------+
| instr("aaaaaaabbbbbbcccccc", "f") |
+-----------------------------------+
|                                 0 |
+-----------------------------------+

-- ucase()和lcase()
mysql> select ucase("aaBBccDD123");
+----------------------+
| ucase("aaBBccDD123") |
+----------------------+
| AABBCCDD123          |
+----------------------+
1 row in set (0.08 sec)

mysql> select lcase("aaBBccDD123");
+----------------------+
| lcase("aaBBccDD123") |
+----------------------+
| aabbccdd123          |
+----------------------+
1 row in set (0.08 sec)

-- left 和 right
mysql> select left("aaBBccDD123", 4);
+------------------------+
| left("aaBBccDD123", 4) |
+------------------------+
| aaBB                   |
+------------------------+
1 row in set (0.07 sec)

mysql> select right("aaBBccDD123", 4);
+-------------------------+
| right("aaBBccDD123", 4) |
+-------------------------+
| D123                    |
+-------------------------+
1 row in set (0.08 sec)
-- 超过了就返回全部
mysql> select right("aaBBccDD123", 1111);
+----------------------------+
| right("aaBBccDD123", 1111) |
+----------------------------+
| aaBBccDD123                |
+----------------------------+
1 row in set (0.10 sec)

-- length()和trim(), utf-8编码 
mysql> select length('t');
+-------------+
| length('t') |
+-------------+
|           1 |
+-------------+
1 row in set (0.08 sec)

mysql> select length('它');
+--------------+
| length('它') |
+--------------+
|            3 |
+--------------+
1 row in set (0.10 sec)

mysql> select length(1);
+-----------+
| length(1) |
+-----------+
|         1 |
+-----------+
1 row in set (0.09 sec)

mysql> select trim("     aaBBccDD1 23   ");
+------------------------------+
| trim("     aaBBccDD1 23   ") |
+------------------------------+
| aaBBccDD1 23                 |
+------------------------------+
1 row in set (0.09 sec)

1.3 在数据库中使用

使用两个表，一个是emp表

一个是exam_result表

1.3.1 获取emp表的ename列的字符集 (charset)

mysql> select charset(ename) from emp;
+----------------+
| charset(ename) |
+----------------+
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
| utf8           |
+----------------+
14 rows in set (0.12 sec)

-- 也可以查查别的列
mysql> select charset(sal) from emp;
+--------------+
| charset(sal) |
+--------------+
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
| binary       |
+--------------+
14 rows in set (0.12 sec)

1.3.2 要求显示exam_result表中的信息 (concat)

显示格式：“XXX的语文是XXX分，数学XXX分，英语XXX分, 总分XXX分”

mysql> select concat(name, "的语文是", chinese, "分, 数学", math, "分, 英语", english, "分, 总分: ", chinese+math+english, "分") msg from exam_result;
+-----------------------------------------------------+
| msg                                                 |
+-----------------------------------------------------+
| 唐三藏的语文是67分, 数学98分, 英语56分, 总分: 221分 |
| 孙悟空的语文是87分, 数学78分, 英语77分, 总分: 242分 |
| 猪悟能的语文是88分, 数学98分, 英语90分, 总分: 276分 |
| 曹孟德的语文是82分, 数学84分, 英语67分, 总分: 233分 |
| 刘玄德的语文是55分, 数学85分, 英语45分, 总分: 185分 |
| 孙权的语文是70分, 数学73分, 英语78分, 总分: 221分   |
| 宋公明的语文是75分, 数学65分, 英语30分, 总分: 170分 |
+-----------------------------------------------------+
7 rows in set (0.17 sec)

1.3.3 替换emp表信息 (replace)

将job列的ERK换成’职员’

mysql> select replace(job, "ERK", "职员") msg from emp;
+-----------+
| msg       |
+-----------+
| CL职员    |
| SALESMAN  |
| SALESMAN  |
| MANAGER   |
| SALESMAN  |
| MANAGER   |
| MANAGER   |
| ANALYST   |
| PRESIDENT |
| SALESMAN  |
| CL职员    |
| CL职员    |
| ANALYST   |
| CL职员    |
+-----------+
14 rows in set (0.12 sec)

1.3.4 截取emp表信息 (substring)

截取EMP表中ename字段的第二个到第三个字符

mysql> select ename from emp;
+--------+
| ename  |
+--------+
| SMITH  |
| ALLEN  |
| WARD   |
| JONES  |
| MARTIN |
| BLAKE  |
| CLARK  |
| SCOTT  |
| KING   |
| TURNER |
| ADAMS  |
| JAMES  |
| FORD   |
| MILLER |
+--------+
14 rows in set (0.12 sec)

mysql> select substring(ename, 2, 2) from emp;
+------------------------+
| substring(ename, 2, 2) |
+------------------------+
| MI                     |
| LL                     |
| AR                     |
| ON                     |
| AR                     |
| LA                     |
| LA                     |
| CO                     |
| IN                     |
| UR                     |
| DA                     |
| AM                     |
| OR                     |
| IL                     |
+------------------------+
14 rows in set (0.12 sec)

1.3.5 以首字母小写的方式显示所有员工的姓名

综合使用

mysql> select concat(lcase(left(ename, 1)), right(ename, length(ename)-1)) from emp;
+--------------------------------------------------------------+
| concat(lcase(left(ename, 1)), right(ename, length(ename)-1)) |
+--------------------------------------------------------------+
| sMITH                                                        |
| aLLEN                                                        |
| wARD                                                         |
| jONES                                                        |
| mARTIN                                                       |
| bLAKE                                                        |
| cLARK                                                        |
| sCOTT                                                        |
| kING                                                         |
| tURNER                                                       |
| aDAMS                                                        |
| jAMES                                                        |
| fORD                                                         |
| mILLER                                                       |
+--------------------------------------------------------------+

3. 数学函数

3.1 部分介绍

函数名	描述
ABS(x)	返回 x 的绝对值
BIN(decimal_num)	将十进制数转为2进制
HEX(decimal_num)	将十进制数转为16进制
CONV(num, fom_base, to_base)	将数字从from_base进制转为to_base进制
CEILING(x)	返回大于或等于 x 的最小整数（向上取整）
FLOOR(x)	返回小于或等于 x 的最大整数（向下取整）
RAND()	返回 0 到 1 的随机数
FORMAT(number, decimal_places)	格式化，保留小数位数
MOD(x,y)	返回 x 除以 y 以后的余数

3.2 基础使用

去绝对值，进制转换，取余

mysql> select abs(-11);
+----------+
| abs(-11) |
+----------+
|       11 |
+----------+
1 row in set (0.05 sec)

mysql> select bin(7);
+--------+
| bin(7) |
+--------+
| 111    |
+--------+
1 row in set (0.06 sec)

mysql> select hex(10);
+---------+
| hex(10) |
+---------+
| A       |
+---------+
1 row in set (0.06 sec)

mysql> select conv(8, 10, 8);
+----------------+
| conv(8, 10, 8) |
+----------------+
| 10             |
+----------------+
1 row in set (0.07 sec)

mysql> select mod(10, 4);
+------------+
| mod(10, 4) |
+------------+
|          2 |
+------------+
1 row in set (0.06 sec)

随机数，格式化

mysql> select rand();
+---------------------+
| rand()              |
+---------------------+
| 0.04022560365519077 |
+---------------------+
1 row in set (0.07 sec)

mysql> select rand() * 100;
+-------------------+
| rand() * 100      |
+-------------------+
| 51.45658315295035 |
+-------------------+
1 row in set (0.09 sec)

mysql> select format(rand() * 100, 0);
+-------------------------+
| format(rand() * 100, 0) |
+-------------------------+
| 45                      |
+-------------------------+
1 row in set (0.09 sec)

mysql> select format(rand() * 100, 2);
+-------------------------+
| format(rand() * 100, 2) |
+-------------------------+
| 71.71                   |
+-------------------------+
1 row in set (0.09 sec)

向上，向下取整

mysql> select ceil(3.1);
+-----------+
| ceil(3.1) |
+-----------+
|         4 |
+-----------+
1 row in set (0.08 sec)

mysql> select ceil(-3.1);
+------------+
| ceil(-3.1) |
+------------+
|         -3 |
+------------+
1 row in set (0.10 sec)

mysql> select floor(3.1);
+------------+
| floor(3.1) |
+------------+
|          3 |
+------------+
1 row in set (0.08 sec)

mysql> select floor(-3.1);
+-------------+
| floor(-3.1) |
+-------------+
|          -4 |
+-------------+
1 row in set (0.10 sec)

4. 其它函数

user() 查询当前用户, database()查询当前用的数据库

mysql> select user();
+--------+
| user() |
+--------+
| root@  |
+--------+
1 row in set (0.06 sec)

mysql> select database();
+------------+
| database() |
+------------+
| testdb     |
+------------+
1 row in set (0.05 sec)

加密函数md5(str)和password(str)

create table t1 (id int primary key auto_increment, password char(32));
Query OK, 0 rows affected (0.05 sec)

mysql> insert into t1 (password) values ("aaaaBBaa11");
Query OK, 1 row affected (0.03 sec)

mysql> insert into t1 (password) values (md5("aaaaBBaa11"));
Query OK, 1 row affected (0.03 sec)

mysql> insert into t1 (password) values (password("aaaaBBaa11"));
Query OK, 1 row affected (0.03 sec)

mysql> select * from t1;
+----+-------------------------------------------+
| id | password                                  |
+----+-------------------------------------------+
|  1 | aaaaBBaa11                                |
|  2 | e574c3309a2fb2a0c239a22fcb4d6f70          |
|  3 | *F582F307B72CA2E12BB3A8B722A34AC223231182 |
+----+-------------------------------------------+

-- 如何查看当前用户的密码输入的正确还是不正确?
mysql> select * from t1 where id = 3 and password = (password('aaaaBBaa11'));
+----+-------------------------------------------+
| id | password                                  |
+----+-------------------------------------------+
|  3 | *F582F307B72CA2E12BB3A8B722A34AC223231182 |
+----+-------------------------------------------+
1 row in set (0.11 sec)

ifnull(val1， val2) 如果val1为null，返回val2，否则返回val1的值

mysql> select ifnull(null, 123);
+-------------------+
| ifnull(null, 123) |
+-------------------+
|               123 |
+-------------------+
1 row in set (0.10 sec)

mysql> select ifnull("abc", 123);
+--------------------+
| ifnull("abc", 123) |
+--------------------+
| abc                |
+--------------------+
1 row in set (0.11 sec)

MySQL 内置函数

1. 日期函数

1.1 部分介绍

1.2 获得当前日期，时间，时间戳，日期时间

1.2 返回datetime的日期部分

1.3 日期加减，日期的差

1.4 示例1，创建一个留言板

2. 字符串函数

1.1 部分介绍

1.2 简单使用

1.3 在数据库中使用

1.3.1 获取emp表的ename列的字符集 (charset)

1.3.2 要求显示exam_result表中的信息 (concat)

1.3.3 替换emp表信息 (replace)

1.3.4 截取emp表信息 (substring)

1.3.5 以首字母小写的方式显示所有员工的姓名

3. 数学函数

3.1 部分介绍

3.2 基础使用

4. 其它函数

悦读

1.2 返回`datetime`的日期部分