MySQL-单行函数:数值函数、字符串函数、日期和时间函数、流程控制函数、加密与解密函数、MySQL信息函数、其他函数、单行函数练习

1.数值函数

1.1 基本的操作

sql 复制代码
SELECT ABS(-123),ABS(32),SIGN(-23),SIGN(43),PI(),CEIL(32.32),CEILING(-43.23),FLOOR(32.32),
FLOOR(-43.23),MOD(12,5),12 MOD 5,12 % 5
FROM DUAL;

1.2 取随机数

sql 复制代码
SELECT RAND(),RAND(),RAND(10),RAND(10),RAND(-1),RAND(-1)
FROM DUAL;

1.3 四舍五入,截断操作

sql 复制代码
SELECT ROUND(123.556),ROUND(123.456,0),ROUND(123.456,1),ROUND(123.456,2),
ROUND(123.456,-1),ROUND(153.456,-2)
FROM DUAL;
sql 复制代码
SELECT TRUNCATE(123.456,0),TRUNCATE(123.496,1),TRUNCATE(129.45,-1)
FROM DUAL;

1.4 单行函数可以嵌套

sql 复制代码
SELECT TRUNCATE(ROUND(123.456,2),0)
FROM DUAL;

1.5 角度与弧度的互换

sql 复制代码
SELECT RADIANS(30),RADIANS(45),RADIANS(60),RADIANS(90),
DEGREES(2*PI()),DEGREES(RADIANS(60))
FROM DUAL;

1.6 三角函数

sql 复制代码
SELECT SIN(RADIANS(30)),DEGREES(ASIN(1)),TAN(RADIANS(45)),DEGREES(ATAN(1))
FROM DUAL;

1.7 指数和对数

sql 复制代码
SELECT POW(2,5),POWER(2,4),EXP(2)
FROM DUAL;
sql 复制代码
SELECT LN(EXP(2)),LOG(EXP(2)),LOG10(10),LOG2(4)
FROM DUAL;

1.8 进制间的转换

sql 复制代码
SELECT BIN(10),HEX(10),OCT(10),CONV(10,10,8)
FROM DUAL;

2. 字符串函数

sql 复制代码
SELECT ASCII('Abcdfsf'),CHAR_LENGTH('hello'),CHAR_LENGTH('我们'),
LENGTH('hello'),LENGTH('我们')
FROM DUAL;

2.1 xxx worked for yyy

sql 复制代码
SELECT CONCAT(emp.last_name,' worked for ',mgr.last_name) "details"
FROM employees emp JOIN employees mgr
WHERE emp.`manager_id` = mgr.employee_id;
sql 复制代码
SELECT CONCAT_WS('-','hello','world','hello','beijing')
FROM DUAL;
sql 复制代码
#字符串的索引是从1开始的!
SELECT INSERT('helloworld',2,3,'aaaaa'),REPLACE('hello','lol','mmm')
FROM DUAL;
sql 复制代码
SELECT UPPER('HelLo'),LOWER('HelLo')
FROM DUAL;
sql 复制代码
SELECT last_name,salary
FROM employees
WHERE LOWER(last_name) = 'King';
sql 复制代码
SELECT LEFT('hello',2),RIGHT('hello',3),RIGHT('hello',13)
FROM DUAL;

2.2 LPAD:实现右对齐效果

2.3 RPAD:实现左对齐效果

sql 复制代码
SELECT employee_id,last_name,LPAD(salary,10,' ')
FROM employees;
sql 复制代码
SELECT CONCAT('---',LTRIM('    h  el  lo   '),'***'),
TRIM('oo' FROM 'ooheollo')
FROM DUAL;
sql 复制代码
SELECT REPEAT('hello',4),LENGTH(SPACE(5)),STRCMP('abc','abe')
FROM DUAL;
sql 复制代码
SELECT SUBSTR('hello',2,2),LOCATE('lll','hello')
FROM DUAL;
sql 复制代码
SELECT ELT(2,'a','b','c','d'),FIELD('mm','gg','jj','mm','dd','mm'),
FIND_IN_SET('mm','gg,mm,jj,dd,mm,gg')
FROM DUAL;
sql 复制代码
SELECT employee_id,NULLIF(LENGTH(first_name),LENGTH(last_name)) "compare"
FROM employees;

3. 日期和时间函数

3.1 获取日期、时间

sql 复制代码
SELECT CURDATE(),CURRENT_DATE(),CURTIME(),NOW(),SYSDATE(),
UTC_DATE(),UTC_TIME()
FROM DUAL;
sql 复制代码
SELECT CURDATE(),CURDATE() + 0,CURTIME() + 0,NOW() + 0
FROM DUAL;

3.2 日期与时间戳的转换

sql 复制代码
SELECT UNIX_TIMESTAMP(),UNIX_TIMESTAMP('2021-10-01 12:12:32'),
FROM_UNIXTIME(1635173853),FROM_UNIXTIME(1633061552)
FROM DUAL;

3.3 获取月份、星期、星期数、天数等函数

sql 复制代码
SELECT YEAR(CURDATE()),MONTH(CURDATE()),DAY(CURDATE()),
HOUR(CURTIME()),MINUTE(NOW()),SECOND(SYSDATE())
FROM DUAL;
sql 复制代码
SELECT MONTHNAME('2021-10-26'),DAYNAME('2021-10-26'),WEEKDAY('2021-10-26'),
QUARTER(CURDATE()),WEEK(CURDATE()),DAYOFYEAR(NOW()),
DAYOFMONTH(NOW()),DAYOFWEEK(NOW())
FROM DUAL;

3.4 日期的操作函数

sql 复制代码
SELECT EXTRACT(SECOND FROM NOW()),EXTRACT(DAY FROM NOW()),
EXTRACT(HOUR_MINUTE FROM NOW()),EXTRACT(QUARTER FROM '2021-05-12')
FROM DUAL;

3.5 时间和秒钟转换的函数

sql 复制代码
SELECT TIME_TO_SEC(CURTIME()),
SEC_TO_TIME(83355)
FROM DUAL;

3.6 计算日期和时间的函数

sql 复制代码
SELECT NOW(),DATE_ADD(NOW(),INTERVAL 1 YEAR),
DATE_ADD(NOW(),INTERVAL -1 YEAR),
DATE_SUB(NOW(),INTERVAL 1 YEAR)
FROM DUAL;
sql 复制代码
SELECT DATE_ADD(NOW(), INTERVAL 1 DAY) AS col1,DATE_ADD('2021-10-21 23:32:12',INTERVAL 1 SECOND) AS col2,
ADDDATE('2021-10-21 23:32:12',INTERVAL 1 SECOND) AS col3,
DATE_ADD('2021-10-21 23:32:12',INTERVAL '1_1' MINUTE_SECOND) AS col4,
DATE_ADD(NOW(), INTERVAL -1 YEAR) AS col5, #可以是负数
DATE_ADD(NOW(), INTERVAL '1_1' YEAR_MONTH) AS col6 #需要单引号
FROM DUAL;
sql 复制代码
SELECT ADDTIME(NOW(),20),SUBTIME(NOW(),30),SUBTIME(NOW(),'1:1:3'),DATEDIFF(NOW(),'2021-10-01'),
TIMEDIFF(NOW(),'2021-10-25 22:10:10'),FROM_DAYS(366),TO_DAYS('0000-12-25'),
LAST_DAY(NOW()),MAKEDATE(YEAR(NOW()),32),MAKETIME(10,21,23),PERIOD_ADD(20200101010101,10)
FROM DUAL;

3.7 日期的格式化与解析

格式化:日期 ---> 字符串
解析: 字符串 ----> 日期
此时我们谈的是日期的显式格式化和解析
之前,我们接触过隐式的格式化或解析

sql 复制代码
SELECT *
FROM employees
WHERE hire_date = '1993-01-13';

#格式化:

sql 复制代码
SELECT DATE_FORMAT(CURDATE(),'%Y-%M-%D'),
DATE_FORMAT(NOW(),'%Y-%m-%d'),TIME_FORMAT(CURTIME(),'%h:%i:%S'),
DATE_FORMAT(NOW(),'%Y-%M-%D %h:%i:%S %W %w %T %r')
FROM DUAL;

解析:格式化的逆过程

sql 复制代码
SELECT STR_TO_DATE('2021-October-25th 11:37:30 Monday 1','%Y-%M-%D %h:%i:%S %W %w')
FROM DUAL;
sql 复制代码
SELECT GET_FORMAT(DATE,'USA')
FROM DUAL;
sql 复制代码
SELECT DATE_FORMAT(CURDATE(),GET_FORMAT(DATE,'USA'))
FROM DUAL;

4.流程控制函数

4.1 IF(VALUE,VALUE1,VALUE2)

sql 复制代码
SELECT last_name,salary,IF(salary >= 6000,'高工资','低工资') "details"
FROM employees;
sql 复制代码
SELECT last_name,commission_pct,IF(commission_pct IS NOT NULL,commission_pct,0) "details",
salary * 12 * (1 + IF(commission_pct IS NOT NULL,commission_pct,0)) "annual_sal"
FROM employees;

4.2 IFNULL(VALUE1,VALUE2):看做是IF(VALUE,VALUE1,VALUE2)的特殊情况

sql 复制代码
SELECT last_name,commission_pct,IFNULL(commission_pct,0) "details"
FROM employees;

4.3 CASE WHEN ... THEN ...WHEN ... THEN ... ELSE ... END

类似于java的if ... else if ... else if ... else

sql 复制代码
SELECT last_name,salary,CASE WHEN salary >= 15000 THEN '白骨精' 
			     WHEN salary >= 10000 THEN '潜力股'
			     WHEN salary >= 8000 THEN '小屌丝'
			     ELSE '草根' END "details",department_id
FROM employees;
sql 复制代码
SELECT last_name,salary,CASE WHEN salary >= 15000 THEN '白骨精' 
			     WHEN salary >= 10000 THEN '潜力股'
			     WHEN salary >= 8000 THEN '小屌丝'
			     END "details"
FROM employees;

4.4 CASE ... WHEN ... THEN ... WHEN ... THEN ... ELSE ... END

类似于java的swich ... case...
练习1

查询部门号为 10,20, 30 的员工信息,

若部门号为 10, 则打印其工资的 1.1 倍,

20 号部门, 则打印其工资的 1.2 倍,

30 号部门,打印其工资的 1.3 倍数,

其他部门,打印其工资的 1.4 倍数

sql 复制代码
SELECT employee_id,last_name,department_id,salary,CASE department_id WHEN 10 THEN salary * 1.1
								     WHEN 20 THEN salary * 1.2
								     WHEN 30 THEN salary * 1.3
								     ELSE salary * 1.4 END "details"
FROM employees;

练习2

查询部门号为 10,20, 30 的员工信息,

若部门号为 10, 则打印其工资的 1.1 倍,

20 号部门, 则打印其工资的 1.2 倍,

30 号部门打印其工资的 1.3 倍数

sql 复制代码
SELECT employee_id,last_name,department_id,salary,CASE department_id WHEN 10 THEN salary * 1.1
								     WHEN 20 THEN salary * 1.2
								     WHEN 30 THEN salary * 1.3
								     END "details"
FROM employees
WHERE department_id IN (10,20,30);

5. 加密与解密的函数

PASSWORD()在mysql8.0中弃用。

sql 复制代码
SELECT MD5('mysql'),SHA('mysql'),MD5(MD5('mysql'))
FROM DUAL;

ENCODE()\DECODE() 在mysql8.0中弃用。

复制代码
SELECT ENCODE('atguigu','mysql'),DECODE(ENCODE('atguigu','mysql'),'mysql')
FROM DUAL;

6. MySQL信息函数

sql 复制代码
SELECT VERSION(),CONNECTION_ID(),DATABASE(),SCHEMA(),
USER(),CURRENT_USER(),CHARSET('尚硅谷'),COLLATION('尚硅谷')
FROM DUAL;

7. 其他函数

#如果n的值小于或者等于0,则只保留整数部分

sql 复制代码
SELECT FORMAT(123.125,2),FORMAT(123.125,0),FORMAT(123.125,-2)
FROM DUAL;
sql 复制代码
SELECT CONV(16, 10, 2), CONV(8888,10,16), CONV(NULL, 10, 2)
FROM DUAL;

以"192.168.1.100"为例,计算方式为192乘以256的3次方,加上168乘以256的2次方,加上1乘以256,再加上100。

sql 复制代码
SELECT INET_ATON('192.168.1.100'),INET_NTOA(3232235876)
FROM DUAL;

BENCHMARK()用于测试表达式的执行效率

sql 复制代码
SELECT BENCHMARK(100000,MD5('mysql'))
FROM DUAL;

CONVERT():可以实现字符集的转换

sql 复制代码
SELECT CHARSET('atguigu'),CHARSET(CONVERT('atguigu' USING 'gbk'))
FROM DUAL;

8.单行函数-练习

1.显示系统时间(注:日期+时间)

sql 复制代码
SELECT NOW() 
FROM DUAL;

2.查询员工号,姓名,工资,以及工资提高百分之20%后的结果(new salary)

sql 复制代码
SELECT employee_id, last_name, salary, salary * 1.2 "new salary" 
FROM employees;

3.将员工的姓名按首字母排序,并写出姓名的长度(length)

sql 复制代码
SELECT last_name, LENGTH(last_name) 
FROM employees 
ORDER BY last_name 
DESC;

4.查询员工id,last_name,salary,并作为一个列输出,别名为OUT_PUT

sql 复制代码
SELECT CONCAT(employee_id, ',' , last_name , ',', salary) OUT_PUT 
FROM employees;

5.查询公司各员工工作的年数、工作的天数,并按工作年数的降序排序。 commission_pct不为空

sql 复制代码
SELECT DATEDIFF(NOW(),e.hire_date)/365 work_years,DATEDIFF(NOW(),e.hire_date) work_days
from employees e
ORDER BY work_years DESC;

6.查询员工姓名,hire_date , department_id,
满足以下条件:雇用时间在 1997年之后,department_id 为80 或 90 或110, commission_pct不为空

sql 复制代码
SELECT e.last_name,e.hire_date,e.department_id
from employees e
-- where hire_date>='1997-01-1' 
-- WHERE DATE_FORMAT(NOW(),'%Y')>= '1997'
where hire_date>=STR_TO_DATE('1997-01-01','%Y-%m-%d')
and department_id in(80,90,110) 
AND commission_pct is not null;

7.查询公司中入职超过10000天的员工姓名、入职时间

sql 复制代码
SELECT last_name,hire_date
from employees
-- where DATEDIFF(NOW(),hire_date)>10000;
WHERE TO_DAYS(NOW())-TO_DAYS(hire_date)>10000;

8.做一个查询,产生下面的结果

sql 复制代码
SELECT CONCAT(last_name,' earns ',salary,' monthly but wants ',TRUNCATE(salary*3,0)) "Dream Salary"
from employees;
sql 复制代码
SELECT last_name Last_name, job_id Job_id,CASE job_id when 'AD_PRES' then 'A'
                                                      when 'ST_MAN' then 'A'
                                                      when 'IT_PROG' then 'A'
                                                      when ' SA_REP' then 'A'
                                                      ELSE 'E'
                                                      END "Grade"
FROM employees;
相关推荐
feifeigo1231 小时前
升级到MySQL 8.4,MySQL启动报错:io_setup() failed with EAGAIN
数据库·mysql·adb
火龙谷2 小时前
【nosql】有哪些非关系型数据库?
数据库·nosql
焱焱枫3 小时前
Oracle获取执行计划之10046 技术详解
数据库·oracle
qq_392397125 小时前
Redis常用操作
数据库·redis·wpf
A__tao6 小时前
一键将 SQL 转为 Java 实体类,全面支持 MySQL / PostgreSQL / Oracle!
java·sql·mysql
一只fish6 小时前
MySQL 8.0 OCP 1Z0-908 题目解析(17)
数据库·mysql
花好月圆春祺夏安7 小时前
基于odoo17的设计模式详解---装饰模式
数据库·python·设计模式
A__tao7 小时前
SQL 转 Java 实体类工具
java·数据库·sql
m0_653031367 小时前
腾讯云认证考试报名 - TDSQL数据库交付运维专家(TCCE PostgreSQL版)
运维·数据库·腾讯云
叁沐8 小时前
MySQL 06 全局锁和表锁:给表加个字段怎么有这么多阻碍?
mysql