6-MySQL_表的内置函数

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1.日期函数

1.1 获取日期函数

bash 复制代码

获得年月日
mysql> select current_date();
+----------------+
| current_date() |
+----------------+
| 2026-03-18     |
+----------------+
1 row in set (0.00 sec)

获得时分秒
mysql> select current_time();
+----------------+
| current_time() |
+----------------+
| 18:07:07       |
+----------------+
1 row in set (0.00 sec)

获得时间戳
mysql> select current_timestamp();
+---------------------+
| current_timestamp() |
+---------------------+
| 2026-03-18 18:07:17 |
+---------------------+
1 row in set (0.00 sec)

获取datetime参数的日期部分
mysql> select date(current_timestamp());
+---------------------------+
| date(current_timestamp()) |
+---------------------------+
| 2026-03-18                |
+---------------------------+
1 row in set (0.00 sec)

1.2 日期计算

bash 复制代码

日期的基础上加上时间
mysql> select date_add('2020-10-10',interval 10 day);
+----------------------------------------+
| date_add('2020-10-10',interval 10 day) |
+----------------------------------------+
| 2020-10-20                             |
+----------------------------------------+
1 row in set (0.00 sec)

日期的基础上减去时间
mysql> select date_sub('2020-10-10',interval 10 day);
+----------------------------------------+
| date_sub('2020-10-10',interval 10 day) |
+----------------------------------------+
| 2020-09-30                             |
+----------------------------------------+
1 row in set (0.00 sec)

获取日期之间相差多少
mysql> select datediff('2020-10-10','2019-10-10');
+-------------------------------------+
| datediff('2020-10-10','2019-10-10') |
+-------------------------------------+
|                                 366 |
+-------------------------------------+
1 row in set (0.00 sec)

案例1：

注意current_time插入date类型的参数时，会转变成当前日期

bash 复制代码

mysql> insert into tmp(birthday) values(current_date());
Query OK, 1 row affected (0.00 sec)

mysql> insert into tmp(birthday) values(current_time());
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> select * from tmp;
+----+------------+
| id | birthday   |
+----+------------+
|  1 | 2026-03-18 |
|  2 | 2026-03-18 |
+----+------------+
2 rows in set (0.00 sec)

案例2：

我们发留言时，我们的评论会附带显示日期

bash 复制代码

创建留言
mysql> create table msg(
    -> id int primary key auto_increment,
    -> content varchar(30) not null,
    -> sendtime datetime);
Query OK, 0 rows affected (0.00 sec)

mysql> insert into msg(content,sendtime) values('hello1', now());
Query OK, 1 row affected (0.00 sec)

mysql> insert into msg(content,sendtime) values('hello2', now());
Query OK, 1 row affected (0.00 sec)

mysql> select * from msg;
+----+---------+---------------------+
| id | content | sendtime            |
+----+---------+---------------------+
|  1 | hello1  | 2026-03-18 18:20:07 |
|  2 | hello2  | 2026-03-18 18:20:10 |
+----+---------+---------------------+
2 rows in set (0.00 sec)
查询两分钟内的留言
mysql> select * from msg where date_add(sendtime,interval 2 minute) > now();
+----+---------+---------------------+
| id | content | sendtime            |
+----+---------+---------------------+
|  1 | hello1  | 2026-03-18 18:20:07 |
|  2 | hello2  | 2026-03-18 18:20:10 |
+----+---------+---------------------+
2 rows in set (0.00 sec)

2. 字符串函数

2.1 charset 返回字符串字符集

bash 复制代码

mysql> select charset(name) from students;
+---------------+
| charset(name) |
+---------------+
| utf8          |
| utf8          |
| utf8          |
| utf8          |
+---------------+
4 rows in set (0.00 sec)

2.2 concat连接字符串

bash 复制代码

mysql> select concat(name,'的语文是',chinese,'分,数学是',math,'分,英语是',english,'分') as '分数' from exam_result;
+-----------------------------------------------------------+
| 分数                                                      |
+-----------------------------------------------------------+
| 唐三藏的语文是67分,数学是98分,英语是56分                  |
| 猪悟能的语文是88分,数学是98分,英语是90分                  |
| 曹孟德的语文是70分,数学是90分,英语是67分                  |
| 刘玄德的语文是55分,数学是115分,英语是45分                 |
| 孙权的语文是70分,数学是73分,英语是78分                    |
| 宋公明的语文是75分,数学是95分,英语是30分                  |
+-----------------------------------------------------------+
6 rows in set (0.00 sec)

2.3 length计算string的长度

bash 复制代码

mysql> select length(name) ,name from exam_result;
+--------------+-----------+
| length(name) | name      |
+--------------+-----------+
|            9 | 唐三藏    |
|            9 | 猪悟能    |
|            9 | 曹孟德    |
|            9 | 刘玄德    |
|            6 | 孙权      |
|            9 | 宋公明    |
+--------------+-----------+
6 rows in set (0.00 sec)

注意：**length函数返回字符串长度，以字节为单位。**如果是多字节字符则计算多个字节数；如果是单字节字符则算作一个字节。比如：字母，数字算作一个字节，中文表示多个字节数（与字符集编码有关）

2.4 replace替换字符

bash 复制代码

mysql> select * from emp;
+--------+--------+-----------+------+---------------------+---------+---------+--------+
| empno  | ename  | job       | mgr  | hiredate            | sal     | comm    | deptno |
+--------+--------+-----------+------+---------------------+---------+---------+--------+
| 007369 | SMITH  | CLERK     | 7902 | 1980-12-17 00:00:00 |  800.00 |    NULL |     20 |
| 007499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 00:00:00 | 1600.00 |  300.00 |     30 |
| 007521 | WARD   | SALESMAN  | 7698 | 1981-02-22 00:00:00 | 1250.00 |  500.00 |     30 |
| 007566 | JONES  | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 |    NULL |     20 |
| 007654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |     30 |
| 007698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 |    NULL |     30 |
| 007782 | CLARK  | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 |    NULL |     10 |
| 007788 | SCOTT  | ANALYST   | 7566 | 1987-04-19 00:00:00 | 3000.00 |    NULL |     20 |
| 007839 | KING   | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |    NULL |     10 |
| 007844 | TURNER | SALESMAN  | 7698 | 1981-09-08 00:00:00 | 1500.00 |    0.00 |     30 |
| 007876 | ADAMS  | CLERK     | 7788 | 1987-05-23 00:00:00 | 1100.00 |    NULL |     20 |
| 007900 | JAMES  | CLERK     | 7698 | 1981-12-03 00:00:00 |  950.00 |    NULL |     30 |
| 007902 | FORD   | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 |    NULL |     20 |
| 007934 | MILLER | CLERK     | 7782 | 1982-01-23 00:00:00 | 1300.00 |    NULL |     10 |
+--------+--------+-----------+------+---------------------+---------+---------+--------+
14 rows in set (0.00 sec)

mysql> select replace(ename,'S','北京'),ename from emp;
+-----------------------------+--------+
| replace(ename,'S','北京')   | ename  |
+-----------------------------+--------+
| 北京MITH                    | SMITH  |
| ALLEN                       | ALLEN  |
| WARD                        | WARD   |
| JONE北京                    | JONES  |
| MARTIN                      | MARTIN |
| BLAKE                       | BLAKE  |
| CLARK                       | CLARK  |
| 北京COTT                    | SCOTT  |
| KING                        | KING   |
| TURNER                      | TURNER |
| ADAM北京                    | ADAMS  |
| JAME北京                    | JAMES  |
| FORD                        | FORD   |
| MILLER                      | MILLER |
+-----------------------------+--------+
14 rows in set (0.00 sec)

2.5 ucase与lcase转换大小写

bash 复制代码

mysql> select lcase(ename),ename from emp;
+--------------+--------+
| lcase(ename) | ename  |
+--------------+--------+
| smith        | SMITH  |
| allen        | ALLEN  |
| ward         | WARD   |
| jones        | JONES  |
| martin       | MARTIN |
| blake        | BLAKE  |
| clark        | CLARK  |
| scott        | SCOTT  |
| king         | KING   |
| turner       | TURNER |
| adams        | ADAMS  |
| james        | JAMES  |
| ford         | FORD   |
| miller       | MILLER |
+--------------+--------+
14 rows in set (0.00 sec)

mysql> select ucase(lcase(ename)),ename from emp;
+---------------------+--------+
| ucase(lcase(ename)) | ename  |
+---------------------+--------+
| SMITH               | SMITH  |
| ALLEN               | ALLEN  |
| WARD                | WARD   |
| JONES               | JONES  |
| MARTIN              | MARTIN |
| BLAKE               | BLAKE  |
| CLARK               | CLARK  |
| SCOTT               | SCOTT  |
| KING                | KING   |
| TURNER              | TURNER |
| ADAMS               | ADAMS  |
| JAMES               | JAMES  |
| FORD                | FORD   |
| MILLER              | MILLER |
+---------------------+--------+
14 rows in set (0.00 sec)

2.6 substring 截取length个字符

bash 复制代码

以首字母小写的方式显示所有员工的姓名
mysql> select concat(lcase(substring(ename,1,1)),substring(ename,2)) ,ename from emp;
+--------------------------------------------------------+--------+
| concat(lcase(substring(ename,1,1)),substring(ename,2)) | ename  |
+--------------------------------------------------------+--------+
| sMITH                                                  | SMITH  |
| aLLEN                                                  | ALLEN  |
| wARD                                                   | WARD   |
| jONES                                                  | JONES  |
| mARTIN                                                 | MARTIN |
| bLAKE                                                  | BLAKE  |
| cLARK                                                  | CLARK  |
| sCOTT                                                  | SCOTT  |
| kING                                                   | KING   |
| tURNER                                                 | TURNER |
| aDAMS                                                  | ADAMS  |
| jAMES                                                  | JAMES  |
| fORD                                                   | FORD   |
| mILLER                                                 | MILLER |
+--------------------------------------------------------+--------+
14 rows in set (0.00 sec)

2.7 ltrim、trim、rtrim去除前后空格

bash 复制代码

mysql> select ltrim('      hello!       ') ltrim,trim('       hello!       ') trim , rtrim('       hello!      ') rtrim;
+---------------+--------+---------------+
| ltrim         | trim   | rtrim         |
+---------------+--------+---------------+
| hello!        | hello! |        hello! |
+---------------+--------+---------------+
1 row in set (0.00 sec)

3. 数学函数

3.1 abs绝对值

bash 复制代码

mysql> select abs(-1),abs(1.1);
+---------+----------+
| abs(-1) | abs(1.1) |
+---------+----------+
|       1 |      1.1 |
+---------+----------+
1 row in set (0.00 sec)

3.2 bin、hex进制的转换

bash 复制代码

mysql> select bin(10),hex(10);
+---------+---------+
| bin(10) | hex(10) |
+---------+---------+
| 1010    | A       |
+---------+---------+
1 row in set (0.00 sec)

3.3 conv任意进制的转换

bash 复制代码

mysql> select conv(10,10,2);
+---------------+
| conv(10,10,2) |
+---------------+
| 1010          |
+---------------+
1 row in set (0.00 sec)

mysql> select conv(10,10,16);
+----------------+
| conv(10,10,16) |
+----------------+
| A              |
+----------------+
1 row in set (0.00 sec)

3.4 ceiling向上取整、floor向下取整

bash 复制代码

mysql> select ceiling(23.04),floor(23.7);
+----------------+-------------+
| ceiling(23.04) | floor(23.7) |
+----------------+-------------+
|             24 |          23 |
+----------------+-------------+
1 row in set (0.00 sec)

3.5 format格式化保留小数位数

bash 复制代码

mysql> select format(12.3456,2);
+-------------------+
| format(12.3456,2) |
+-------------------+
| 12.35             |
+-------------------+
1 row in set (0.00 sec)

3.6 rand产生随机数

bash 复制代码

mysql> select rand();
+---------------------+
| rand()              |
+---------------------+
| 0.12839327112621932 |
+---------------------+
1 row in set (0.00 sec)

0~100的随机数
mysql> select rand()*100;
+-------------------+
| rand()*100        |
+-------------------+
| 34.58598790186084 |
+-------------------+
1 row in set (0.00 sec)

3.7 mod取模求余

bash 复制代码

mysql> select mod(12,3);
+-----------+
| mod(12,3) |
+-----------+
|         0 |
+-----------+
1 row in set (0.00 sec)

mysql> select mod(12,5);
+-----------+
| mod(12,5) |
+-----------+
|         2 |
+-----------+
1 row in set (0.00 sec)

4.其他函数

4.1 user查询当前用户

bash 复制代码

mysql> select user();
+--------+
| user() |
+--------+
| root@  |
+--------+
1 row in set (0.00 sec)

4.2 md5

bash 复制代码

mysql> create table user(
    -> name varchar(20),
    -> password varchar(32));
Query OK, 0 rows affected (0.00 sec)

mysql> select * from user where name = '张三'and password = md5('11111111111111');
+--------+----------------------------------+
| name   | password                         |
+--------+----------------------------------+
| 张三   | e78582c7fa761cb9358009503f2810a9 |
+--------+----------------------------------+
1 row in set (0.00 sec)

4.3 password用户加密

bash 复制代码

mysql> select password('root');
+-------------------------------------------+
| password('root')                          |
+-------------------------------------------+
| *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B |
+-------------------------------------------+
1 row in set, 1 warning (0.00 sec)

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

bash 复制代码

mysql> select ifnull('abc','123');
+---------------------+
| ifnull('abc','123') |
+---------------------+
| abc                 |
+---------------------+
1 row in set (0.00 sec)

mysql> select ifnull(null,'123');
+--------------------+
| ifnull(null,'123') |
+--------------------+
| 123                |
+--------------------+
1 row in set (0.00 sec)

6-MySQL_表的内置函数

1.日期函数

1.1 获取日期函数

1.2 日期计算

2. 字符串函数

2.1 charset 返回字符串字符集

2.2 concat连接字符串

2.3 length计算string的长度

2.4 replace替换字符

2.5 ucase与lcase转换大小写

2.6 substring 截取length个字符

2.7 ltrim、trim、rtrim去除前后空格

3. 数学函数

3.1 abs绝对值

3.2 bin、hex进制的转换

3.3 conv任意进制的转换

3.4 ceiling向上取整、floor向下取整

3.5 format格式化保留小数位数

3.6 rand产生随机数

3.7 mod取模求余

4.其他函数

4.1 user查询当前用户

4.2 md5

4.3 password用户加密

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

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