MySQL 常用函数

1.字符串函数

函数	功能
concat(s1,s2,…,sn)	连接字符串
insert(str,x,y,instr)	将字符串str从第x位置开始，y个字符串替换为字符串instr
lower(str)	将字符串变成小写。类似函数为upper
left(str,x)	返回字符串最左边的x个字符。类似函数为right
Lpad(str,n,pad)	用字符串Pad 对str最左边填充，直到长度为 n个字符长度。类似函数为rpad
Ltrim(str)	去掉字符串str左侧的空格。类似函数 rtrim，trim
Repeat(str,x)	返回字符串Str 重复x次的结果
Replace(str,a,b)	用字符串b替换字符串  str 中所有出现的字符串 a
Strcmp(s1,s2)	比较字符串s1 s2 的ASCII码值的大小
Substring(str,x,y)	返回从字符串str x 位置起y个字符长度的内容

 

连接字符串

SELECT CONCAT('hello','world','!'),CONCAT('world','null');

+-----------------------------+------------------------+

| CONCAT('hello','world','!')   | CONCAT('world','null') |

+-----------------------------+------------------------+

| helloworld!                         | worldnull                    |

+-----------------------------+------------------------+

1 ROW IN SET (0.00 sec)

 

从x位置替换y个字符

SELECT INSERT('china greatwall',7,9,'baiyun');

+----------------------------------------+

| insert('china greatwall',7,9,'baiyun')    |

+----------------------------------------+

| china baiyun                                      |

+----------------------------------------+

1 row in set (0.00 sec)

 

大小写转换

SELECT LOWER('greatWaLL'),UPPER('greatWaLL');

+--------------------+--------------------+

| LOWER('greatWaLL') | UPPER('greatWaLL') |

+--------------------+--------------------+

| greatwall               | GREATWALL          |

+--------------------+--------------------+

1 row in set (0.00 sec)

 

LEFT(STR,X)和RIGHT(STR,X)函数：分别返回字符串最左边的x个字符和最右边的x个字符。

如果第二个参数是null，那么将不反回任何字符串。

SELECT LEFT('greatwall',7),LEFT('greatwall',NULL),RIGHT('greatwall',4);

+---------------------+------------------------+----------------------+

| LEFT('greatwall',7)   | LEFT('greatwall',NULL) | RIGHT('greatwall',4) |

+---------------------+------------------------+----------------------+

| greatwa                  | NULL                          | wall                         |

+---------------------+------------------------+----------------------+

1 row in set (0.00 sec)

 

LPAD(STR,n,pad)和RPAD(str,n,pad)函数：用字符串pad对str最左边和最右边进行填充，知道长度为n个字符长度

SELECT LPAD('great',20,'wall'),RPAD('great',20,'wall');

+-------------------------+-------------------------+

| LPAD('great',20,'wall')    | RPAD('great',20,'wall')  |

+-------------------------+-------------------------+

| wallwallwallwalgreat     | greatwallwallwallwal    |

+-------------------------+-------------------------+

1 row in set (0.01 sec)

 

LIRIM(STR)和RTRIM(STR)函数：去掉字符串str左侧和右侧的空格

SELECT LTRIM('  |great wall|  '),RTRIM('  |greate wall|  ');

+---------------------------+----------------------------+

| LTRIM('  |great wall|  ')     | RTRIM('  |greate wall|  ')    |

+---------------------------+----------------------------+

| |great wall|                       |   |greate wall|                   |

+---------------------------+----------------------------+

1 row in set (0.00 sec)

 

repeat(str,x)函数：返回str重复X次结果

SELECT REPEAT('mysql ',3);

+--------------------+

| REPEAT('mysql ',3) |

+--------------------+

| mysql mysql mysql |

+--------------------+

1 row in set (0.00 sec)

 

REPLACE(STR,a,b)函数：用常用字符串b替换字符串str中所有出现的字符串a

SELECT REPLACE('beijing_2008','_2008','2008');

+----------------------------------------+

| REPLACE('beijing_2008','_2008','2008') |

+----------------------------------------+

| beijing2008                                        |

+----------------------------------------+

1 row in set (0.00 sec)

 

STRCMP(s1,s2)函数：比较字符串S1和S2的ASCII码值的大小

SELECT STRCMP('a','b'),STRCMP('b','b'),STRCMP('c','b');

+-----------------+-----------------+-----------------+

| STRCMP('a','b')  | STRCMP('b','b') | STRCMP('c','b') |

+-----------------+-----------------+-----------------+

|              -1         |               0        |               1         |

+-----------------+-----------------+-----------------+

1 row in set (0.00 sec)

 

trim(str)函数：去掉目标字符串开头和即为的空格

SELECT TRIM('    |beijing2008|    ');

+-------------------------------+

| TRIM('    |beijing2008|    ')      |

+-------------------------------+

| |beijing2008|                          |

+-------------------------------+

1 row in set (0.01 sec)

 

substring(str,x,y)函数：返回从字符串str中的第x位置起y个字符长度的字符串

SELECT SUBSTRING('beijign2008',8,4);

+------------------------------+

| SUBSTRING('beijign2008',8,4) |

+------------------------------+

| 2008                                    |

+------------------------------+

1 row in set (0.00 sec)

 

2.数值函数

函数	功能
ABS(X)	返回X的绝对值
CEIL(X)	返回大于X的最小整数值
FLOOR(X)	返回小于X的最大整数值
MOD(X,Y)	返回X/Y的模
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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ABS(X)函数，返回绝对值

SELECT ABS(1),ABS(-1);

+--------+---------+

| ABS(1)  | ABS(-1)   |

+--------+---------+

|      1      |       1     |

+--------+---------+

1 row in set (0.00 sec)

 

CEIL(x)函数：返回大于x的最小整数值

SELECT CEIL(-0.8),CEIL(0.8);

+------------+-----------+

| CEIL(-0.8)    | CEIL(0.8)   |

+------------+-----------+

|          0        |         1      |

+------------+-----------+

1 row in set (0.00 sec)

 

FLOOR(X)函数：返回小鱼X的最大整数，和CEIL的用法想反

SELECT FLOOR(-0.8),FLOOR(0.8);

+-------------+------------+

| FLOOR(-0.8) | FLOOR(0.8) |

+-------------+------------+

|          -1       |          0       |

+-------------+------------+

1 row in set (0.01 sec)

 

MOD(x,y)函数：返回X/Y的模

模数和被模数的任何一个味NULL结果都为NULL，例如：
SELECT MOD(15,10),MOD(1,11),MOD(NULL,10);

+------------+-----------+--------------+

| MOD(15,10) | MOD(1,11) | MOD(NULL,10) |

+------------+-----------+--------------+

|          5       |         1       |         NULL    |

+------------+-----------+--------------+

1 row in set (0.01 sec)

 

RAND()函数：返回0~1内的随机数

SELECT RAND(),RAND();

+------------------+--------------------+

| RAND()               | RAND()                 |

+------------------+--------------------+

| 0.73975877532713 | 0.5370678152302911 |

+------------------+--------------------+

1 row in set (0.00 sec)

 

SELECT RAND()*100,RAND()*100;

+-------------------+-------------------+

| RAND()*100          | RAND()*100         |

+-------------------+-------------------+

| 46.60627809037108 | 71.91104895613253 |

+-------------------+-------------------+

1 row in set (0.00 sec)

1~100的随即整数

SELECT CEIL(RAND()*100),CEIL(RAND()*100);

+------------------+------------------+

| CEIL(RAND()*100) | CEIL(RAND()*100) |

+------------------+------------------+

|               20         |               83        |

+------------------+------------------+

1 row in set (0.00 sec)

 

ROUNAD(x,y)函数：返回参数X的四舍五入的有y为小数的值

SELECT ROUND(1.5),ROUND(1.55,1),ROUND(111,2),ROUND(1.1,2);

+------------+---------------+--------------+--------------+

| ROUND(1.5) | ROUND(1.55,1) | ROUND(111,2) | ROUND(1.1,2) |

+------------+---------------+--------------+--------------+

|          2       |           1.6        |          111     |         1.10      |

+------------+---------------+--------------+--------------+

1 row in set (0.00 sec)

 

TRUNCATE(X,Y)函数：返回数字X截断为Y位小数的结果（非四舍五入）

SELECT ROUND(1.235,2),TRUNCATE(1.235,2);

+----------------+-------------------+

| ROUND(1.235,2) | TRUNCATE(1.235,2) |

+----------------+-------------------+

|           1.24        |              1.23        |

+----------------+-------------------+

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()	返回当前时间和日期
UNIX_TIMESTAMP(date)	返回日期date的UNIX时间戳
FROM_UNIXTIME	返回UNIX时间戳的日期值
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分钟值
MONTHNAME(date)	返回date的月份名
DATE_FORMAT(date,fmt)	返回字符串fmt格式化日期  date值
DATE_ADD(date,interval expr type)	返回一个日期或时间值加上一个时间间隔的时间值
DATEDIFF(expr1,expr2)	返回起始时间expr1 和结束时间 expr2之间的天数

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CURDATE()函数：返回当前日期，只包含年月日，同CURRENT_DATE()

SELECT CURDATE(),CURRENT_DATE();

+------------+----------------+

| CURDATE()  | CURRENT_DATE() |

+------------+----------------+

| 2012-12-04 | 2012-12-04     |

+------------+----------------+

1 row in set (0.00 sec)

 

URTIME()函数：返回当前时间，只包含时分秒，同CURRENT_TIME()

SELECT CURTIME(),CURRENT_TIME();

+-----------+----------------+

| CURTIME() | CURRENT_TIME() |

+-----------+----------------+

| 16:10:48    | 16:10:48           |

+-----------+----------------+

1 row in set (0.00 sec)

 

NOW()函数：返回当前的日期和时间

SELECT NOW();

+---------------------+

| NOW()                    |

+---------------------+

| 2012-12-04 16:11:43 |

+---------------------+

1 row in set (0.00 sec)

 

UNIX_TIMESTAMP(date)函数：返回日期date的UNIX时间戳。

SELECT UNIX_TIMESTAMP(NOW());

+-----------------------+

| UNIX_TIMESTAMP(NOW()) |

+-----------------------+

|            1354608756    |

+-----------------------+

1 row in set (0.00 sec)

 

FROM_UNIXTIME(unixtime)函数：返回UNIXTIME时间戳的日期值，和UNIX_TIMESTAMP(date)互为逆操作

SELECT FROM_UNIXTIME(1354608756);

+---------------------------+

| FROM_UNIXTIME(1354608756) |

+---------------------------+

| 2012-12-04 16:12:36       |

+---------------------------+

1 row in set (0.00 sec)

 

week(date)、year(date)、month(date)、day(date)、hour(date)、minute(date)和second(date)函数：

SELECT WEEK(NOW()),YEAR(NOW()),MONTH(NOW()),DAY(NOW()),HOUR(NOW()),MINUTE(NOW()),SECOND(NOW()) ;

+-------------+-------------+--------------+------------+-------------+---------------+---------------+

| WEEK(NOW()) | YEAR(NOW()) | MONTH(NOW()) | DAY(NOW()) | HOUR(NOW()) | MINUTE(NOW()) | SECOND(NOW()) |

+-------------+-------------+--------------+------------+-------------+---------------+---------------+

|          49       |        2012     |           12       |          4      |          16      |            15       |           15       |

+-------------+-------------+--------------+------------+-------------+---------------+---------------+

1 row in set (0.00 sec)

 

date_format(date,fmt)函数：按字符串fmt 格式化日期date值，例如：

将下面的例子按照月，日，年的格式显示：

SELECT DATE_FORMAT(NOW(),‘%M,%D,%Y’);

+-------------------------------+

| DATE_FORMAT(NOW(),'%M,%D,%Y') |

+-------------------------------+

| December,4th,2012             |

+-------------------------------+

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时间段的日期。

其中interval是间隔类型关键字，expr 是一个表达式，这个表达式对应后面的类型，type 是间隔类型， 有如下类型：HOUR、MINUTE、SECOND、YEAR、MONTH、DAY、YEAR_MONTH、DAY_HOUR、DAY_MINUTE、DAY_SECOND、HOUR_MINUTE、HOUR_SECOND和MINUTE_SCOND

 

下面第一列是当前日期，第二列是31天以后的日期，第三列是一年二个月后的日期

SELECT NOW(),DATE_ADD(NOW(),INTERVAL 31 DAY) after31days,DATE_ADD(NOW(),INTERVAL '1_2' YEAR_MONTH) after_oneyear_twomonth;

 +---------------------+---------------------+------------------------+

| NOW()                     | after31days             | after_oneyear_twomonth |

+---------------------+---------------------+------------------------+

| 2012-12-04 16:22:30 | 2013-01-04 16:22:30 | 2014-02-04 16:22:30    |

+---------------------+---------------------+------------------------+

1 row in set (0.00 sec)

 

同样也可以用负数让它返回之前的某个日期时间，如第1列返回了当前日期时间，第2列返回距离当前日期31天前的日期时间，第3列返回距离当前日期一年两个月前的日期时间。

SELECT NOW(),DATE_ADD(NOW(),INTERVAL -31 DAY) after31days,DATE_ADD(NOW(),INTERVAL '-1_-2' YEAR_MONTH) after_oneyear_twomonth;

 +---------------------+---------------------+------------------------+

| NOW()                | after31days          | after_oneyear_twomonth |

+---------------------+---------------------+------------------------+

| 2012-12-04 16:24:19 | 2012-11-03 16:24:19 | 2011-10-04 16:24:19    |

+---------------------+---------------------+------------------------+

1 row in set (0.00 sec)

 

DATEDIFF(date1,date2)函数：计算两个日期之间相关的天数。

下面的例子计算出2012/1/1距今天有多少天

SELECT DATEDIFF(NOW(),'2012-01-01');

+------------------------------+

| DATEDIFF(NOW(),'2012-01-01') |

+------------------------------+

|                          338             |

+------------------------------+

1 row in set (0.01 sec)

 

4.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,vale2)	如果value1不为空返回 value1，否则返回 value2
case when [value1] then [result1]…else [default] end	如果value1是真，返回 result1 ，否则返回default
case [expr] when [value1] then [result1]…else [default] end	如果expr等于value1，返回 result1 ，否则返回default ，这个主要用于等值比较，不适合范围比较

 

创建练习表

CREATE TABLE salary(userid INT,salary DECIMAL(9,2));

Query OK, 0 rows affected (0.04 sec)

 

INSERT INTO salary VALUES(1,1000),(2,2000),(3,3000),(4,4000),(5,5000),(6,NULL);

Query OK, 6 rows affected (0.01 sec)

Records: 6  Duplicates: 0  Warnings: 0

 

SELECT * FROM salary;

+--------+---------+

| userid | salary  |

+--------+---------+

|      1 | 1000.00 |

|      2 | 2000.00 |

|      3 | 3000.00 |

|      4 | 4000.00 |

|      5 | 5000.00 |

|      6 |    NULL |

+--------+---------+

6 rows in set (0.00 sec)

 

if(vale,t ,f) 函数：这里认为月薪在2000元以上的职员属于高薪，用“high”表示；而2000以下属于低薪，用“low”表示

SELECT userid,salary,IF(salary>2000,'high','low') FROM salary;

+--------+---------+------------------------------+

| userid   | salary     | IF(salary>2000,'high','low') |

+--------+---------+------------------------------+

|      1     | 1000.00 | low                                       |

|      2     | 2000.00 | low                                       |

|      3     | 3000.00 | high                                     |

|      4     | 4000.00 | high                                     |

|      5     | 5000.00 | high                                     |

|      6     |    NULL | low                                       |

+--------+---------+------------------------------+

6 rows in set (0.00 sec)

 

ifnull(value1,value2)函数：用来替换NULL值

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)

 

CASE WHEN [value1] THEN [result1]…ELSE [DEFAULT] end 当薪水低于2000时，显示LOW，低于3000时，为MID，其于为HIGH

INSERT INTO salary VALUES(7,500),(8,1500),(9,2500);

SELECT userid,salary,CASE WHEN salary<=2000 THEN 'low' WHEN salary<=3000 THEN 'mid' ELSE 'high' END FROM salary WHERE salary IS NOT NULL;

+--------+---------+--------------------------------------------------------------------------------+

| userid | salary  | CASE WHEN salary<=2000 THEN 'low' WHEN salary<=3000 THEN 'mid' ELSE 'high' END |

+--------+---------+--------------------------------------------------------------------------------+

|      1 | 1000.00 | low                                                                            |

|      2 | 2000.00 | low                                                                            |

|      3 | 3000.00 | mid                                                                            |

|      4 | 4000.00 | high                                                                           |

|      5 | 5000.00 | high                                                                           |

|      7 |  500.00  | low                                                                            |

|      8 | 1500.00 | low                                                                            |

|      9 | 2500.00 | mid                                                                            |

+--------+---------+--------------------------------------------------------------------------------+

8 rows in set (0.00 sec) 

 

CASE [expr] WHEN [value1] THEN [result1]…ELSE [DEFAULT] end 当值等于values1，返回result1,值为values2，返回result2…

下面的例子中，userid =3 ，显示pen , userid =5 ，显示pencil ,其余的显示book

SELECT userid,salary,CASE userid WHEN 3 THEN 'pen' WHEN 5 THEN 'pencil' ELSE 'book' END FROM salary

+--------+---------+--------------------------------------------------------------------+

| userid | salary  | CASE userid WHEN 3 THEN 'pen' WHEN 5 THEN 'pencil' ELSE 'book' END |

+--------+---------+--------------------------------------------------------------------+

|      1 | 1000.00 | book                                                               |

|      2 | 2000.00 | book                                                               |

|      3 | 3000.00 | pen                                                                |

|      4 | 4000.00 | book                                                               |

|      5 | 5000.00 | pencil                                                             |

|      6 |    NULL | book                                                               |

|      7 |  500.00  | book                                                               |

|      8 | 1500.00 | book                                                               |

|      9 | 2500.00 | book                                                               |

+--------+---------+--------------------------------------------------------------------+

9 rows in set (0.00 sec)

 

5.常用函数

函数	功能
database()	返回当前数据库名
version()	返回当前数据库版本
user()	返回当前用户登陆名

 

 

 

 

 

 

 

 

USE test;

SELECT DATABASE();

SELECT VERSION();

SELECT USER();