MySQL 常用函数
1. 字符串函数
| 函数 | 功能 |
|---|---|
| concat(s1,s2,…,sn) | 连接s1,s2,…,sn为一个字符串 |
| insert(str,x,y,instr) | 将字符串str从第x位置开始，y个字符长的子串替换为字符串instr（位置从1开始） |
| lower(str) | 将字符串str中的字符转换成小写 |
| upper(str) | 将字符串str中的字符转换成大写 |
| left(str,x) | 返回str最左边的x个字符 |
| right(str,x) | 返回str最右边的x个字符 |
| lpad(str,n,pad) | 用字符串pad对str最左边进行填充，直到长度为n个字符长度 |
| rpad(str,n,pad) | 用字符串pad对str最右边进行填充，直到长度为n个字符长度 |
| ltrim(str) | 去掉左侧的空格 |
| rtrim(str) | 去掉右侧的空格 |
| trim(str) | 去掉两侧的空格 |
| repeat(str,n) | 返回字符串str重复n次的结果 |
| replace(str,a,b) | 用b替换str中所有出现的a |
| strcmp(s1,s2) | 比较两个字符串s1,s2。返回1，0，-1 |
| substring(str,x,y) | 返回从字符串str的x位置起的y个字符长度的子串（位置从1开始） |
2. 数值函数
| 函数 | 功能 |
|---|---|
| abs(x) | 绝对值 |
| ceil(x) | 返回大于x的最小整数值，即向上取整 |
| floor(x) | 返回小于x的最大整数值，即向下取整 |
| mod(x,y) | x对y取余 |
| rand() | 返回0~1内的随机值 |
| round(x,y) | 返回参数x的四舍五入的有y位小数的值 |
| truncate(x,y) | 返回数字x截断为y位小数的结果 |
eg.
mysql> select ceil(1.2), floor(1.2);
+-----------+------------+
| ceil(1.2) | floor(1.2) |
+-----------+------------+
| 2 | 1 |
+-----------+------------+
1 row in set (0.00 sec)
mysql> select ceil(-1.2), floor(-1.2);
+------------+-------------+
| ceil(-1.2) | floor(-1.2) |
+------------+-------------+
| -1 | -2 |
+------------+-------------+
1 row in set (0.00 sec)
mysql> select rand(), ceil(100*rand());
+--------------------+------------------+
| rand() | ceil(100*rand()) |
+--------------------+------------------+
| 0.6494681040285789 | 24 |
+--------------------+------------------+
1 row in set (0.00 sec)
mysql> select round(1.2345,2), round(1.456, 2);
+-----------------+-----------------+
| round(1.2345,2) | round(1.456, 2) |
+-----------------+-----------------+
| 1.23 | 1.46 |
+-----------------+-----------------+
1 row in set (0.00 sec)
mysql> select round(1.2345,6), round(1.456, 6);
+-----------------+-----------------+
| round(1.2345,6) | round(1.456, 6) |
+-----------------+-----------------+
| 1.234500 | 1.456000 |
+-----------------+-----------------+
1 row in set (0.00 sec)
mysql> select strcmp('bb', 'aa'), strcmp('bb', 'bb'), strcmp('bb', 'cc');
+--------------------+--------------------+--------------------+
| strcmp('bb', 'aa') | strcmp('bb', 'bb') | strcmp('bb', 'cc') |
+--------------------+--------------------+--------------------+
| 1 | 0 | -1 |
+--------------------+--------------------+--------------------+
1 row in set (0.00 sec)
mysql> select truncate(1.2345, 3), truncate(1.2345, 6);
+---------------------+---------------------+
| truncate(1.2345, 3) | truncate(1.2345, 6) |
+---------------------+---------------------+
| 1.234 | 1.234500 |
+---------------------+---------------------+
1 row in set (0.00 sec)
3. 日期和时间函数
| 函数 | 功能 |
|---|---|
| curdate() | 返回当前日期 |
| curtime() | 返回当前时间 |
| now() | 返回当前日期和时间 |
| unix_timestamp(date) | 返回日期date的unix时间戳 |
| from_unixtime(stamp) | 返回时间戳stamp的日期值 |
| week(date) | 返回日期date为一年中的第几周 |
| year(date) | 返回date的年份 |
| hour(time) | 返回time的小时值 |
| minute(time) | 返回time的分钟值 |
| monthname(date) | 显示date的月份名 |
| date_format(date,fmt) | 格式化日期时间 |
| date_add(date,INTERVAL expr type) | 返回与所给日期date加上INTERVAL 时间段的日期 |
| date_sub(date, INTERVAL expr type) | 返回与所给日期date减去INTERVAL 时间段的日期 |
| datediff(date1,date2) | 计算两个日期之间相差的天数。date1-date2的天数 |
eg.
mysql> select curdate();
+------------+
| curdate() |
+------------+
| 2018-10-27 |
+------------+
1 row in set (0.00 sec)
mysql> select curtime();
+-----------+
| curtime() |
+-----------+
| 21:45:00 |
+-----------+
1 row in set (0.00 sec)
mysql> select now();
+---------------------+
| now() |
+---------------------+
| 2018-10-27 21:45:22 |
+---------------------+
1 row in set (0.00 sec)
mysql> select unix_timestamp(now());
+-----------------------+
| unix_timestamp(now()) |
+-----------------------+
| 1540648073 |
+-----------------------+
1 row in set (0.00 sec)
mysql> select from_unixtime(1540648073);
+---------------------------+
| from_unixtime(1540648073) |
+---------------------------+
| 2018-10-27 21:47:53 |
+---------------------------+
1 row in set (0.00 sec)
mysql> select week(now());
+-------------+
| week(now()) |
+-------------+
| 42 |
+-------------+
1 row in set (0.00 sec)
mysql> select year(now());
+-------------+
| year(now()) |
+-------------+
| 2018 |
+-------------+
1 row in set (0.00 sec)
mysql> select hour(now());
+-------------+
| hour(now()) |
+-------------+
| 22 |
+-------------+
1 row in set (0.00 sec)
mysql> select minute(now());
+---------------+
| minute(now()) |
+---------------+
| 4 |
+---------------+
1 row in set (0.00 sec)
mysql> select monthname(now());
+------------------+
| monthname(now()) |
+------------------+
| October |
+------------------+
1 row in set (0.00 sec)
date_format(date, fmt):
按照字符串fmt 格式化日期 date 值，此函数能够按指定的格式显示日期，可以用到的格式符如下表显示：
| 格式符 | 格式说明 |
|---|---|
| %S和%s | 两位数字形式的秒(00,01,…,59) |
| %i | 两位数字形式的分(00,01,…,59) |
| %H | 两位数字形式的小时，24小时(00,01,…,23) |
| %h和%I(大写i) | 两位数字形式的小时，12小时(01,02,…,12) |
| %k | 数字形式的小时，24小时(0,1,…,23) |
| %l(小写L) | 数字形式的小时，12小时(1,2,…,12) |
| %T | 24小时的时间形式(hh:mm:ss) |
| %r | 12小时的时间格式(hh:mm:ssAM或hh:mm:ssPM) |
| %p | AM 或 PM |
| %W | 一周中每一天的名称(Sunday,Monday,…,Saturday) |
| %a | 一周中每一天名称的缩写(Sun,Mon,…,Sat) |
| %w | 以数字形式表示周中的天数(0=Sunday,1=Monday,…,6=Saturday) |
| %d | 两位数字表示月中的天数(01,…,31) |
| %e | 数字形式表示月中的天数(1,2,…,31) |
| %D | 英文后缀表示月中的天数(1st,2nd,3rd,…) |
| %j | 以3位数字表示年中的天数(001,002,…,366) |
| %U | 一年中的第几周(00,01,…,52)，其中Sunday为周中的第一天。（从00开始） |
| %u | 一年中的第几周(01,02,…,53)，其中Monday为周中的第一天。（从01开始） |
| %M | 月名(January,February,…,December) |
| %b | 缩写的月名(Jan,Feb,…,Dec) |
| %m | 两位数字表示的月份(01,02,…,12) |
| %c | 数字表示的月份(1,2,…,12) |
| %Y | 4位数字表示的年份(2018) |
| %y | 两位数字表示的年份(18) |
eg.
mysql> select date_format(now(), '%M, %D, %Y');
+----------------------------------+
| date_format(now(), '%M, %D, %Y') |
+----------------------------------+
| October, 27th, 2018 |
+----------------------------------+
1 row in set (0.00 sec)
时间：
mysql> select date_format(now(), '%H:%i:%S, %H:%i:%s');
+------------------------------------------+
| date_format(now(), '%H:%i:%S, %H:%i:%s') |
+------------------------------------------+
| 23:27:02, 23:27:02 |
+------------------------------------------+
1 row in set (0.00 sec)
mysql> select date_format(now(), '%h:%i:%S %p, %I:%i:%S %p');
+------------------------------------------------+
| date_format(now(), '%h:%i:%S %p, %I:%i:%S %p') |
+------------------------------------------------+
| 11:27:54 PM, 11:27:54 PM |
+------------------------------------------------+
1 row in set (0.00 sec)
mysql> select date_format(now(), '%k:%i:%S, %l:%i:%S %p');
+---------------------------------------------+
| date_format(now(), '%k:%i:%S, %l:%i:%S %p') |
+---------------------------------------------+
| 23:28:57, 11:28:57 PM |
+---------------------------------------------+
1 row in set (0.00 sec)
mysql> select date_format(now(), '%T, %r');
+------------------------------+
| date_format(now(), '%T, %r') |
+------------------------------+
| 23:29:32, 11:29:32 PM |
+------------------------------+
1 row in set (0.00 sec)
星期几：
mysql> select date_format(now(), '%W %a %w');
+--------------------------------+
| date_format(now(), '%W %a %w') |
+--------------------------------+
| Saturday Sat 6 |
+--------------------------------+
1 row in set (0.00 sec)
日期天数：
mysql> select date_format(now(), '%d, %e, %D');
+----------------------------------+
| date_format(now(), '%d, %e, %D') |
+----------------------------------+
| 27, 27, 27th |
+----------------------------------+
1 row in set (0.00 sec)
第几天和第几周：
mysql> select date_format('2018-01-01', '%j, %U, %u, %W');
+---------------------------------------------+
| date_format('2018-01-01', '%j, %U, %u, %W') |
+---------------------------------------------+
| 001, 00, 01, Monday |
+---------------------------------------------+
1 row in set (0.00 sec)
mysql> select date_format('2018-12-31', '%j, %U, %u, %W');
+---------------------------------------------+
| date_format('2018-12-31', '%j, %U, %u, %W') |
+---------------------------------------------+
| 365, 52, 53, Monday |
+---------------------------------------------+
1 row in set (0.00 sec)
月份名：
mysql> select date_format('2018-01-01', '%M, %b, %m, %c');
+---------------------------------------------+
| date_format('2018-01-01', '%M, %b, %m, %c') |
+---------------------------------------------+
| January, Jan, 01, 1 |
+---------------------------------------------+
1 row in set (0.00 sec)
年份：
mysql> select date_format('2018-01-01', '%Y, %y');
+-------------------------------------+
| date_format('2018-01-01', '%Y, %y') |
+-------------------------------------+
| 2018, 18 |
+-------------------------------------+
1 row in set (0.00 sec)
date_add(date, interval expr type) 函数： 返回与所给日期 date 相差 INTERVAL 的时间段的日期。
其中 INTERVAL 是间隔类型的关键字，expr 是一个表达式，正数表示向后加这个间隔，负数则表示向前减去这个间隔。这个表达式对应后面的类型，type 是间隔类型，MySQL 提供了 13 种间隔类型，如下表：
| 表达式类型 | 描述 |
|---|---|
| hour | 小时 |
| minute | 分钟 |
| second | 秒 |
| year | 年 |
| month | 月 |
| day | 日 |
| year_month | 年和月 |
| day_hour | 日和小时 |
| day_minute | 日和分钟 |
| day_second | 日和秒 |
| hour_minute | 小时和分钟 |
| hour_second | 小时和秒 |
| minute_second | 分钟和秒 |
eg.
mysql> select now() current, date_add(now(), interval 1 hour) after1hour;
+---------------------+---------------------+
| current | after1hour |
+---------------------+---------------------+
| 2018-10-28 11:22:24 | 2018-10-28 12:22:24 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval 1 minute) after1minute;
+---------------------+---------------------+
| current | after1minute |
+---------------------+---------------------+
| 2018-10-28 11:22:43 | 2018-10-28 11:23:43 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval 1 second) after1second;
+---------------------+---------------------+
| current | after1second |
+---------------------+---------------------+
| 2018-10-28 11:23:13 | 2018-10-28 11:23:14 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval 1 year) after1year;
+---------------------+---------------------+
| current | after1year |
+---------------------+---------------------+
| 2018-10-28 11:23:43 | 2019-10-28 11:23:43 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval 1 month) after1month;
+---------------------+---------------------+
| current | after1month |
+---------------------+---------------------+
| 2018-10-29 21:39:03 | 2018-11-29 21:39:03 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval 1 day) after1day;
+---------------------+---------------------+
| current | after1day |
+---------------------+---------------------+
| 2018-10-29 21:39:14 | 2018-10-30 21:39:14 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval '1_1' year_month) after1year1month;
+---------------------+---------------------+
| current | after1year1month |
+---------------------+---------------------+
| 2018-10-28 11:26:11 | 2019-11-28 11:26:11 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval '-1_-1' year_month) before1year1month;
+---------------------+---------------------+
| current | before1year1month |
+---------------------+---------------------+
| 2018-10-28 11:30:42 | 2017-09-28 11:30:42 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval '1_1' day_hour) after1day1hour;
+---------------------+---------------------+
| current | after1day1hour |
+---------------------+---------------------+
| 2018-10-28 11:31:15 | 2018-10-29 12:31:15 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval '1_1' day_minute) after1day1minute;
+---------------------+---------------------+
| current | after1day1minute |
+---------------------+---------------------+
| 2018-10-28 11:31:29 | 2018-10-28 12:32:29 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval '1_1' day_second) after1day1second;
+---------------------+---------------------+
| current | after1day1second |
+---------------------+---------------------+
| 2018-10-28 11:31:42 | 2018-10-28 11:32:43 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval '1_1' hour_minute) after1hour1minute;
+---------------------+---------------------+
| current | after1hour1minute |
+---------------------+---------------------+
| 2018-10-28 11:32:04 | 2018-10-28 12:33:04 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval '1_1' hour_second) after1hour1second;
+---------------------+---------------------+
| current | after1hour1second |
+---------------------+---------------------+
| 2018-10-28 11:32:29 | 2018-10-28 11:33:30 |
+---------------------+---------------------+
1 row in set (0.00 sec)
mysql> select now() current, date_add(now(), interval '1_1' minute_second) after1minute1second;
+---------------------+---------------------+
| current | after1minute1second |
+---------------------+---------------------+
| 2018-10-28 11:32:44 | 2018-10-28 11:33:45 |
+---------------------+---------------------+
1 row in set (0.00 sec)
date_sub(date, INTERVAL expr type)：返回与所给日期date减去INTERVAL 时间段的日期。
eg.
mysql> select now() current, date_sub(now(), interval 1 day) before1day;
+---------------------+---------------------+
| current | before1day |
+---------------------+---------------------+
| 2018-10-29 21:40:09 | 2018-10-28 21:40:09 |
+---------------------+---------------------+
1 row in set (0.00 sec)
datediff(date1, date2): 计算两个日期之间相差的天数。date1-date2
eg. 表示当前距离2010-09-14已经过去了2966天。
mysql> select now() current, datediff(now(), '2010-09-14');
+---------------------+-------------------------------+
| current | datediff(now(), '2010-09-14') |
+---------------------+-------------------------------+
| 2018-10-28 11:35:02 | 2966 |
+---------------------+-------------------------------+
1 row in set (0.00 sec)
4. 流程函数
流程函数也是很常用的一类函数，用户可以使用这类函数在一个SQL语句中实现条件选择，这样做能够提高语句的效率。
MySQL 中的流程函数
| 函数 | 功能 |
|---|---|
| if(value, t, f) | 如果 value 是真，返回t；否则返回f |
| ifnull(value1, value2) | 如果 value1 不为空，返回value1，否则返回 value2 |
| case when [value1] then [result]…else[default] end | 多条件判断，见eg.相当于if…else if… else if … else |
| case [expr] when [value] then [result]…else[default] end | 多值判断，见eg. case A…;case B…;… default |
eg.
创建职员薪水表：
mysql> create table salary(userid int, salary decimal(9,2));
Query OK, 0 rows affected (0.08 sec)
mysql> insert into salary values(1,1000),(2,2000),(3,3000),(4,4000),(5,5000),(1,null);
Query OK, 6 rows affected (0.03 sec)
Records: 6 Duplicates: 0 Warnings: 0
mysql> select * from salary;
+--------+---------+
| userid | salary |
+--------+---------+
| 1 | 1000.00 |
| 2 | 2000.00 |
| 3 | 3000.00 |
| 4 | 4000.00 |
| 5 | 5000.00 |
| 1 | NULL |
+--------+---------+
6 rows in set (0.00 sec)
各个函数：
mysql> select if(salary > 2000, 'high','low') from salary;
+---------------------------------+
| if(salary > 2000, 'high','low') |
+---------------------------------+
| low |
| low |
| high |
| high |
| high |
| low |
+---------------------------------+
6 rows in set (0.00 sec)
mysql> select ifnull(salary,0) from salary;
+------------------+
| ifnull(salary,0) |
+------------------+
| 1000.00 |
| 2000.00 |
| 3000.00 |
| 4000.00 |
| 5000.00 |
| 0.00 |
+------------------+
6 rows in set (0.00 sec)
mysql> select case when salary<=2000 then 'low' when salary<=3000 then 'middle' else 'high' end from salary;
+------------------------------------------------------------------------------------+
| case when salary<=2000 then 'low' when salary<=3000 then 'middle' else 'high' end |
+------------------------------------------------------------------------------------+
| low |
| low |
| middle |
| high |
| high |
| high |
+------------------------------------------------------------------------------------+
6 rows in set (0.00 sec)
mysql> select case salary when 1000 then 'low' when 2000 then 'middle' else 'high' end from salary;
+---------------------------------------------------------------------------+
| case salary when 1000 then 'low' when 2000 then 'middle' else 'high' end |
+---------------------------------------------------------------------------+
| low |
| middle |
| high |
| high |
| high |
| high |
+---------------------------------------------------------------------------+
6 rows in set (0.00 sec)
5. 其他常用函数
| 函数 | 功能 |
|---|---|
| datebase() | 返回当前数据库名 |
| version() | 返回当前数据库版本 |
| user() | 返回当前登录用户名 |
| inet_aton(ip) | 返回ip地址的数字表示 |
| inet_ntoa(num) | 返回数字代表的ip地址 |
| password(str)（8.0.11版本已经移除该函数） | 返回字符串str的加密版本 |
| md5(str) | 返回字符串str的md5值 |
eg.
mysql> select database();
+------------+
| database() |
+------------+
| db201810 |
+------------+
1 row in set (0.00 sec)
mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.11 |
+-----------+
1 row in set (0.00 sec)
mysql> select user();
+--------------------+
| user() |
+--------------------+
| bearyang@localhost |
+--------------------+
1 row in set (0.00 sec)
mysql> select inet_aton('192.168.1.2');
+--------------------------+
| inet_aton('192.168.1.2') |
+--------------------------+
| 3232235778 |
+--------------------------+
1 row in set (0.00 sec)
mysql> select inet_ntoa(3232235778);
+-----------------------+
| inet_ntoa(3232235778) |
+-----------------------+
| 192.168.1.2 |
+-----------------------+
1 row in set (0.01 sec)
# 8.0.11 版本
mysql> select password('123456');
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '('123456')' at line 1
# 5.7.22 版本
mysql> select password('123456');
+-------------------------------------------+
| password('123456') |
+-------------------------------------------+
| *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+-------------------------------------------+
1 row in set, 1 warning (0.00 sec)
mysql> select md5('123456');
+----------------------------------+
| md5('123456') |
+----------------------------------+
| e10adc3949ba59abbe56e057f20f883e |
+----------------------------------+
1 row in set (0.00 sec)