在MySQL中,函数不仅可以出现在select语句及其子句中,而且还可以出现在update、delete语句中。本文主要介绍了MySQL中的常用函数的相关资料,需要的朋友可以参考下,希望能帮助到大家。
常用的函数有:
1. 字符串函数;主要用于处理字符串。
2. 数值函数;主要用于处理数字。
3. 日期和时间函数;主要用于处理日期和事件。
4. 系统信息函数;获取系统信息。
1. 使用字符串函数:
虽然每种数据库都支持SQL,但是每种数据库拥有各自所支持的函数。
1.1 合并字符串函数concat() 和 concat_ws():
在MySQL中可以通过函数concat()和concat_ws()将传入的参数连接成为一个字符串。
语法定义为:
示例:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | mysql> select concat( 'my' , 's' , 'ql' );
+-----------------------+
| concat( 'my' , 's' , 'ql' ) |
+-----------------------+
| mysql |
+-----------------------+
1 row in set (0.00 sec)
mysql> select concat( 'my' , 's' , 'ql' ,null);
+----------------------------+
| concat( 'my' , 's' , 'ql' ,null) |
+----------------------------+
| NULL |
+----------------------------+
1 row in set (0.00 sec)
mysql> select concat(curdate(), 12.2);
+-------------------------+
| concat(curdate(), 12.2) |
+-------------------------+
| 2016-08-2512.2 |
+-------------------------+
1 row in set (0.00 sec)
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concat_ws()的定义:
1 2 3 | concat_ws(sep,s1,s2,...sn)
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示例:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | mysql> select concat_ws( '-' , '020' , '87658907' );
+---------------------------------+
| concat_ws( '-' , '020' , '87658907' ) |
+---------------------------------+
| 020-87658907 |
+---------------------------------+
1 row in set (0.00 sec)
mysql> select concat_ws(null, '020' , '87658907' );
+----------------------------------+
| concat_ws(null, '020' , '87658907' ) |
+----------------------------------+
| NULL |
+----------------------------------+
1 row in set (0.00 sec)
mysql> select concat_ws( '-' , '020' ,null, '87658907' );
+--------------------------------------+
| concat_ws( '-' , '020' ,null, '87658907' ) |
+--------------------------------------+
| 020-87658907 |
+--------------------------------------+
1 row in set (0.00 sec)
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1.2 比较字符串大小函数strcmp():
strcmp()定义为:
示例:
1 2 3 4 5 6 7 | mysql> select strcmp ( 'abc' , 'abd' ), strcmp ( 'abc' , 'abc' ), strcmp ( 'abc' , 'abb' );
+---------------------+---------------------+---------------------+
| strcmp ( 'abc' , 'abd' ) | strcmp ( 'abc' , 'abc' ) | strcmp ( 'abc' , 'abb' ) |
+---------------------+---------------------+---------------------+
| -1 | 0 | 1 |
+---------------------+---------------------+---------------------+
1 row in set (0.00 sec)
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1.3 获取字符串长度函数length()和字符数函数char_length():
length()的定义如下:
length(str)
char_length(str)的定义如下:
char_length(str)
示例:
1 2 3 4 5 6 7 8 | mysql> select length( 'mysql' ),length( '汉字' ),char_length( 'mysql' ),char_length( '汉字' );
+-----------------+----------------+----------------------+---------------------+
| length( 'mysql' ) | length( '汉字' ) | char_length( 'mysql' ) | char_length( '汉字' ) |
+-----------------+----------------+----------------------+---------------------+
| 5 | 4 | 5 | 4 |
+-----------------+----------------+----------------------+---------------------+
1 row in set, 2 warnings (0.00 sec)
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1.4 字母的大小写转换upper()和lower():
字母大小转换函数:upper(s); ucase(s);
字母小写转换函数:lower(s); lcase(s);
示例:
1 2 3 4 5 6 7 | mysql> select upper( 'mysql' ),ucase( 'mYsql' ),lower( 'MYSQL' ),lcase( 'MYsql' );
+----------------+----------------+----------------+----------------+
| upper( 'mysql' ) | ucase( 'mYsql' ) | lower( 'MYSQL' ) | lcase( 'MYsql' ) |
+----------------+----------------+----------------+----------------+
| MYSQL | MYSQL | mysql | mysql |
+----------------+----------------+----------------+----------------+
1 row in set (0.00 sec)
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1.5 查找字符串:
mysql中提供了丰富的函数去查找字符串的位置。分别有find_in_set()函数、field()函数、locate()函数、position()函数和instr()函数。同时还提供了查找指定位置的字符串的函数elt()。
1.5.1 返回字符串位置的find_in_set()函数:
函数定义为:
示例:
1 2 3 4 5 6 7 | mysql> select find_in_set( 'mysql' , 'oracle,mysql,db2' );
+-----------------------------------------+
| find_in_set( 'mysql' , 'oracle,mysql,db2' ) |
+-----------------------------------------+
| 2 |
+-----------------------------------------+
1 row in set (0.00 sec)
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1.5.2 返回指定字符串位置的field()函数:
函数定义为:
示例:
1 2 3 4 5 6 7 | mysql> select field( 'mysql' , 'oracle' , 'db2' , 'redis' , 'mysql' );
+-----------------------------------------------+
| field( 'mysql' , 'oracle' , 'db2' , 'redis' , 'mysql' ) |
+-----------------------------------------------+
| 4 |
+-----------------------------------------------+
1 row in set (0.00 sec)
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1.5.3 返回子字符串相匹配的开始位置:
mysql中有三个函数可以获取子字符串相匹配的开始位置,分别是locate()、position()、instr()函数。
locate(str1,str) //返回参数str中字符串str1的开始位置
position(str1 in str) 和 instr(str,str1)
示例:
1 2 3 4 5 6 7 | mysql> select locate( 'sql' , 'mysql' ),position( 'sql' in 'mysql' ),instr( 'mysql' , 'sql' );
+-----------------------+----------------------------+----------------------+
| locate( 'sql' , 'mysql' ) | position( 'sql' in 'mysql' ) | instr( 'mysql' , 'sql' ) |
+-----------------------+----------------------------+----------------------+
| 3 | 3 | 3 |
+-----------------------+----------------------------+----------------------+
1 row in set (0.00 sec)
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1.5.4 返回指定位置的字符串的elt()函数:
函数语法为:
elt(n,str1,str2...);
示例:
1 2 3 4 5 6 7 | mysql> select elt(1, 'mysql' , 'db2' , 'oracle' );
+-------------------------------+
| elt(1, 'mysql' , 'db2' , 'oracle' ) |
+-------------------------------+
| mysql |
+-------------------------------+
1 row in set (0.00 sec)
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1.5.5 选择字符串的make_set()函数:
函数定义为:
make_set(num,str1,str2...strn)
示例:
1 2 3 4 5 6 7 8 | mysql> select bin(5),make_set(5, 'mysql' , 'db2' , 'oracle' , 'redus' );
+--------+--------------------------------------------+
| bin(5) | make_set(5, 'mysql' , 'db2' , 'oracle' , 'redus' ) |
+--------+--------------------------------------------+
| 101 | mysql,oracle |
+--------+--------------------------------------------+
1 row in set (0.00 sec)
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1.6 从现有字符串中截取子字符串:
截取子字符串的函数有:left(),right(),substring(),mid();
1.6.1 从左边或右边截取子字符串:
函数定义为:
1 2 3 4 | left(str,num)
right(str,num)
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示例:
1 2 3 4 5 6 7 | mysql> select left( 'mysql' ,2),right( 'mysql' ,3);
+-----------------+------------------+
| left( 'mysql' ,2) | right( 'mysql' ,3) |
+-----------------+------------------+
| my | sql |
+-----------------+------------------+
1 row in set (0.00 sec)
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1.6.2 截取指定位置和长度的字符串:
可以通过substring()和mid()函数截取指定位置和长度的字符串。
函数语法为:
1 2 | substring(str,num,len)
mid(str,num,len)
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示例:
1 2 3 4 5 6 7 | mysql> select substring( 'zhaojd' ,2,3),mid( 'zhaojd' ,2,4);
+-------------------------+-------------------+
| substring( 'zhaojd' ,2,3) | mid( 'zhaojd' ,2,4) |
+-------------------------+-------------------+
| hao | haoj |
+-------------------------+-------------------+
1 row in set (0.00 sec)
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1.7 去除字符串的首尾空格:
去除字符串首尾空格的函数有:ltrim()、rtrim()、trim()
1.7.1 去除字符串开始处的空格:
函数定义如下:
ltrim(str) //返回去掉开始处空格的字符串
示例:
1 2 3 4 5 6 7 | mysql> select length(concat( '-' , ' mysql ' , '-' )),length(concat( '-' ,ltrim( ' mysql ' ), '-' ));
+-----------------------------------+------------------------------------------+
| length(concat( '-' , ' mysql ' , '-' )) | length(concat( '-' ,ltrim( ' mysql ' ), '-' )) |
+-----------------------------------+------------------------------------------+
| 9 | 8 |
+-----------------------------------+------------------------------------------+
1 row in set (0.00 sec)
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1.7.2 去除字符串结束处的空格:
rtrim(str) //返回去掉结束处空格的字符串。
示例:
1 2 3 4 5 6 7 | mysql> select length(concat( '-' , ' mysql ' , '-' )) ,length(concat( '-' ,rtrim( ' mysql ' ), '-' ));
+-----------------------------------+------------------------------------------+
| length(concat( '-' , ' mysql ' , '-' )) | length(concat( '-' ,rtrim( ' mysql ' ), '-' )) |
+-----------------------------------+------------------------------------------+
| 9 | 8 |
+-----------------------------------+------------------------------------------+
1 row in set (0.00 sec)
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1.7.3 去除字符串首尾空格:
trim(str) //返回去掉首尾空格的字符串
示例:
1 2 3 4 5 6 7 | mysql> select concat( ' mysql ' ) origi,length(concat( ' mysql ' )) orilen, concat(trim( ' mysql ' )) after, length(concat(trim( ' mysql ' ))) afterlen;
+---------+--------+-------+----------+
| origi | orilen | after | afterlen |
+---------+--------+-------+----------+
| mysql | 7 | mysql | 5 |
+---------+--------+-------+----------+
1 row in set (0.00 sec)
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1.8 替换字符串:
实现替换字符串的功能,分别为insert()和replace()
1.8.1 使用insert()函数:
函数定义为:
insert(str,pos,len,newstr)
//insert()函数会将字符串str中的pos位置开始长度为len的字符串用字符串newstr来替换。
//如果参数pos的值超过字符串长度,则返回值为原始字符串str。
//如果len的长度大于原来str中所剩字符串的长度,则从位置pos开始进行全部替换。若任何一个参数为null,则返回值为null.
示例:
1 2 3 4 5 6 7 | mysql> select insert( '这是mysql数据库系统' ,3,5, 'oracle' ) bieming;
+----------------------+
| bieming |
+----------------------+
| 这oracleql数据库系统 |
+----------------------+
1 row in set, 1 warning (0.00 sec)
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1.8.1 使用replace()函数:
函数的定义为:
replace(str,substr,newstr) //将字符串str中的子字符串substr用字符串newstr来替换。
示例:
1 2 3 4 5 6 7 | mysql> select replace( '这是mysql数据库' , 'mysql' , 'db2' ) bieming;
+---------------+
| bieming |
+---------------+
| 这是db2数据库 |
+---------------+
1 row in set, 1 warning (0.00 sec)
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2. 使用数值函数:
2.1 获取随机数:
通过rand()和rand(x)函数来获取随机数。这两个函数都会返回0-1之间的随机数,其中rand()函数返回的数是完全随机的,而rand(x)函数返回的随机数值是完全相同的。
示例:
1 2 3 4 5 6 7 | mysql> select rand(),rand(),rand(3),rand(3);
+--------------------+--------------------+--------------------+--------------------+
| rand() | rand() | rand(3) | rand(3) |
+--------------------+--------------------+--------------------+--------------------+
| 0.9600886758045188 | 0.7006410161970565 | 0.9057697559760601 | 0.9057697559760601 |
+--------------------+--------------------+--------------------+--------------------+
1 row in set (0.00 sec)
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2.2 获取整数的函数:
在具体应用中,如果想要获取整数,可以通过ceil()和floor()函数来实现。
ceil()函数的定义为:
ceil(x) //函数返回大于或等于数值x的最小整数。
floor() //函数返回小于或等于数值x的最大整数。
示例:
1 2 3 4 5 6 7 | mysql> select ceil (4.3), ceil (-2.5), floor (4.3), floor (-2.5);
+-----------+------------+------------+-------------+
| ceil (4.3) | ceil (-2.5) | floor (4.3) | floor (-2.5) |
+-----------+------------+------------+-------------+
| 5 | -2 | 4 | -3 |
+-----------+------------+------------+-------------+
1 row in set (0.00 sec)
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2.3 截取数值函数:
可以通过truncate()对数值的小数位进行截取:
函数定义为:
truncate(x,y) //返回数值x,保留小数点后y位
示例:
1 2 3 4 5 6 7 | mysql> select truncate(903.343434,2),truncate(903.343,-1);
+------------------------+----------------------+
| truncate(903.343434,2) | truncate(903.343,-1) |
+------------------------+----------------------+
| 903.34 | 900 |
+------------------------+----------------------+
1 row in set (0.00 sec)
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2.4 四舍五入函数:
对数值进行四舍五入可以通过round()函数实现:
round(x)
//函数返回值x经过四舍五入操作后的数值。
round(x,y)
//返回数值x保留到小数点后y位的值。在具体截取数据时需要进行四舍五入的操作。
示例:
1 2 3 4 5 6 7 | mysql> select round (903.53567), round (-903.53567), round (903.53567,2), round (903.53567,-1);
+------------------+-------------------+--------------------+---------------------+
| round (903.53567) | round (-903.53567) | round (903.53567,2) | round (903.53567,-1) |
+------------------+-------------------+--------------------+---------------------+
| 904 | -904 | 903.54 | 900 |
+------------------+-------------------+--------------------+---------------------+
1 row in set (0.00 sec)
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3. 使用日期和时间函数:
3.1 获取当前日期和时间的函数:
3.1.1 获取当前日期和时间(日期 + 时间):
MySQL中可以通过四个函数获取当前日期和时间,分别是now(),current_timestamp(),localtime(),sysdate(),这四个函数不仅可以获取当前日期和时间,而且显示的格式也一样。推荐使用now()
示例:
1 2 3 4 5 6 7 | mysql> select now(),current_timestamp(),localtime(),sysdate();
+---------------------+---------------------+---------------------+---------------------+
| now() | current_timestamp() | localtime() | sysdate() |
+---------------------+---------------------+---------------------+---------------------+
| 2016-08-25 16:09:20 | 2016-08-25 16:09:20 | 2016-08-25 16:09:20 | 2016-08-25 16:09:20 |
+---------------------+---------------------+---------------------+---------------------+
1 row in set (0.00 sec)
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3.1.2 获取当前日期:
获取当前日期的函数curdate()和current_date()函数。
示例:
1 2 3 4 5 6 7 | mysql> select curdate(),current_date();
+------------+----------------+
| curdate() | current_date() |
+------------+----------------+
| 2016-08-25 | 2016-08-25 |
+------------+----------------+
1 row in set (0.00 sec)
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3.1.3 获取当前时间:
获取当前时间的函数,curtime()或者current_time();推荐使用curtime();
示例:
1 2 3 4 5 6 7 | mysql> select curtime(),current_time();
+-----------+----------------+
| curtime() | current_time() |
+-----------+----------------+
| 16:15:04 | 16:15:04 |
+-----------+----------------+
1 row in set (0.00 sec)
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3.2 获取日期和时间各部分值:
在MySQL中,可以通过各种函数来获取当前日期和时间的各部分值,其中year()函数返回日期中的年份,quarter()函数返回日期属于第几个季度,month()函数返回日期属于第几个月,week()函数返回日期属于第几个星期,dayofmonth()函数返回日期属于当前月的第几天,hour()函数返回时间的小时,minute()函数返回时间的分钟,second()函数返回时间的秒。
示例:
1 2 3 4 5 6 7 | mysql> select now(),year(now()),quarter(now()),month(now()),week(now()),dayofmonth(now()),hour(now()),minute(now()),second(now());
+---------------------+-------------+----------------+--------------+-------------+-------------------+-------------+---------------+---------------+
| now() | year(now()) | quarter(now()) | month(now()) | week(now()) | dayofmonth(now()) | hour(now()) | minute(now()) | second(now()) |
+---------------------+-------------+----------------+--------------+-------------+-------------------+-------------+---------------+---------------+
| 2016-08-25 16:27:37 | 2016 | 3 | 8 | 34 | 25 | 16 | 27 | 37 |
+---------------------+-------------+----------------+--------------+-------------+-------------------+-------------+---------------+---------------+
1 row in set (0.00 sec)
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3.2.1 关于月的函数:
示例:
1 2 3 4 5 6 7 8 | mysql> select now(),month(now()),monthname(now());
+---------------------+--------------+------------------+
| now() | month(now()) | monthname(now()) |
+---------------------+--------------+------------------+
| 2016-08-25 16:29:37 | 8 | August |
+---------------------+--------------+------------------+
1 row in set (0.00 sec)
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3.2.2 关于星期的函数:
示例:
1 2 3 4 5 6 7 | mysql> select now(),week(now()),weekofyear(now()),dayname(now()),dayofweek(now()),weekday(now());
+---------------------+-------------+-------------------+----------------+------------------+----------------+
| now() | week(now()) | weekofyear(now()) | dayname(now()) | dayofweek(now()) | weekday(now()) |
+---------------------+-------------+-------------------+----------------+------------------+----------------+
| 2016-08-25 16:34:35 | 34 | 34 | Thursday | 5 | 3 |
+---------------------+-------------+-------------------+----------------+------------------+----------------+
1 row in set (0.00 sec)
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3.2.3 关于天的函数:
示例:
1 2 3 4 5 6 7 | mysql> select now(),dayofyear(now()),dayofmonth(now());
+---------------------+------------------+-------------------+
| now() | dayofyear(now()) | dayofmonth(now()) |
+---------------------+------------------+-------------------+
| 2016-08-25 16:37:12 | 238 | 25 |
+---------------------+------------------+-------------------+
1 row in set (0.00 sec)
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3.2.4 获取指定值的extract():
函数定义为:
示例:
1 2 3 4 5 6 7 8 | mysql> select now(),extract(year from now()) year,extract(month from now()) month,extract(day from now()) day,extract(hour from now()) hour,extract(mi
nute from now()) minute,extract(second from now()) second;
+---------------------+------+-------+------+------+--------+--------+
| now() | year | month | day | hour | minute | second |
+---------------------+------+-------+------+------+--------+--------+
| 2016-08-25 16:43:45 | 2016 | 8 | 25 | 16 | 43 | 45 |
+---------------------+------+-------+------+------+--------+--------+
1 row in set (0.00 sec)
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3.3 计算日期和时间的函数:
3.3.1 与默认日期和时间操作:
两个函数来实现与默认日期和时间的操作,分别为to_days()和from_days()
to_days(date):该函数计算日期参数date与默认日期和时间(0000年1月1日)之间的想个天数。
from_days(number):该函数计算从默认日期和时间(0000年1月1日)开始经历number天后的日期和时间。
示例:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | mysql> select now(),to_days(now()),from_days(to_days(now()));
+---------------------+----------------+---------------------------+
| now() | to_days(now()) | from_days(to_days(now())) |
+---------------------+----------------+---------------------------+
| 2016-08-25 16:50:30 | 736566 | 2016-08-25 |
+---------------------+----------------+---------------------------+
1 row in set (0.00 sec)
mysql> select now(),datediff(now(), '2000-12-01' );
+---------------------+------------------------------+
| now() | datediff(now(), '2000-12-01' ) |
+---------------------+------------------------------+
| 2016-08-25 16:52:16 | 5746 |
+---------------------+------------------------------+
1 row in set (0.00 sec)
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3.3.2 与指定日期和时间操作:
adddate(date,n)函数:该函数计算日期参数date加上n天后的日期。
subdate(date,n)函数:该函数计算日期参数date减去n天后的日期。
adddate(d,interval expr type):返回日期参数d加上一段时间后的日期,表达式参数expr决定了时间的长度,参数type决定了所操作的对象。
subdate(d,interval expr type):返回日期参数d减去一段时间后的日期,表达式expr决定了时间的长度。参数type决定了所操作的对象。
addtime(time,n):计算时间参数time加上n秒后的时间。
subtime(time,n):计算时间参数time减去n秒后的时间。
示例一:
1 2 3 4 5 6 7 | mysql> select curdate(),adddate(curdate(),5),subdate(curdate(),5);
+------------+----------------------+----------------------+
| curdate() | adddate(curdate(),5) | subdate(curdate(),5) |
+------------+----------------------+----------------------+
| 2016-08-25 | 2016-08-30 | 2016-08-20 |
+------------+----------------------+----------------------+
1 row in set (0.00 sec)
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示例二:
1 2 3 4 5 6 7 | mysql> select curdate(),adddate(curdate(),interval '2,3' year_month),subdate(curdate(),interval '2,3' year_month);
+------------+----------------------------------------------+----------------------------------------------+
| curdate() | adddate(curdate(),interval '2,3' year_month) | subdate(curdate(),interval '2,3' year_month) |
+------------+----------------------------------------------+----------------------------------------------+
| 2016-08-25 | 2018-11-25 | 2014-05-25 |
+------------+----------------------------------------------+----------------------------------------------+
1 row in set (0.00 sec)
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示例三:
1 2 3 4 5 6 7 | mysql> select curtime(),addtime(curtime(),5),subtime(curtime(),5);
+-----------+----------------------+----------------------+
| curtime() | addtime(curtime(),5) | subtime(curtime(),5) |
+-----------+----------------------+----------------------+
| 17:12:21 | 17:12:26 | 17:12:16 |
+-----------+----------------------+----------------------+
1 row in set (0.00 sec)
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4. 使用系统信息函数:
1 | select version(),database(),user();
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示例:
1 2 3 4 5 6 7 8 9 | mysql> select version(),database(),user();
+------------+------------+----------------+
| version() | database() | user() |
+------------+------------+----------------+
| 5.5.51-log | NULL | root@localhost |
+------------+------------+----------------+
1 row in set (0.00 sec)
select last_insert_id();
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