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

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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

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SELECT RAND(),RAND(),RAND(10),RAND(10),RAND(-1),RAND(-1)
FROM DUAL;

1.3 四舍五入，截断操作

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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;

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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

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SELECT TRUNCATE(ROUND(123.456,2),0)
FROM DUAL;

1.5 角度与弧度的互换

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

1.6 三角函数

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

1.7 指数和对数

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SELECT POW(2,5),POWER(2,4),EXP(2)
FROM DUAL;

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SELECT LN(EXP(2)),LOG(EXP(2)),LOG10(10),LOG2(4)
FROM DUAL;

1.8 进制间的转换

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SELECT BIN(10),HEX(10),OCT(10),CONV(10,10,8)
FROM DUAL;

2. 字符串函数

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SELECT ASCII('Abcdfsf'),CHAR_LENGTH('hello'),CHAR_LENGTH('我们'),
LENGTH('hello'),LENGTH('我们')
FROM DUAL;

2.1 xxx worked for yyy

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SELECT CONCAT(emp.last_name,' worked for ',mgr.last_name) "details"
FROM employees emp JOIN employees mgr
WHERE emp.`manager_id` = mgr.employee_id;

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SELECT CONCAT_WS('-','hello','world','hello','beijing')
FROM DUAL;

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#字符串的索引是从1开始的！
SELECT INSERT('helloworld',2,3,'aaaaa'),REPLACE('hello','lol','mmm')
FROM DUAL;

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SELECT UPPER('HelLo'),LOWER('HelLo')
FROM DUAL;

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SELECT last_name,salary
FROM employees
WHERE LOWER(last_name) = 'King';

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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

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SELECT employee_id,last_name,LPAD(salary,10,' ')
FROM employees;

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SELECT CONCAT('---',LTRIM('    h  el  lo   '),'***'),
TRIM('oo' FROM 'ooheollo')
FROM DUAL;

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SELECT REPEAT('hello',4),LENGTH(SPACE(5)),STRCMP('abc','abe')
FROM DUAL;

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SELECT SUBSTR('hello',2,2),LOCATE('lll','hello')
FROM DUAL;

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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;

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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

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SELECT CURDATE(),CURRENT_DATE(),CURTIME(),NOW(),SYSDATE(),
UTC_DATE(),UTC_TIME()
FROM DUAL;

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SELECT CURDATE(),CURDATE() + 0,CURTIME() + 0,NOW() + 0
FROM DUAL;

3.2 日期与时间戳的转换

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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

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SELECT YEAR(CURDATE()),MONTH(CURDATE()),DAY(CURDATE()),
HOUR(CURTIME()),MINUTE(NOW()),SECOND(SYSDATE())
FROM DUAL;

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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

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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

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SELECT TIME_TO_SEC(CURTIME()),
SEC_TO_TIME(83355)
FROM DUAL;

3.6 计算日期和时间的函数

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SELECT NOW(),DATE_ADD(NOW(),INTERVAL 1 YEAR),
DATE_ADD(NOW(),INTERVAL -1 YEAR),
DATE_SUB(NOW(),INTERVAL 1 YEAR)
FROM DUAL;

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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;

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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

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SELECT *
FROM employees
WHERE hire_date = '1993-01-13';

#格式化：

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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

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SELECT STR_TO_DATE('2021-October-25th 11:37:30 Monday 1','%Y-%M-%D %h:%i:%S %W %w')
FROM DUAL;

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SELECT GET_FORMAT(DATE,'USA')
FROM DUAL;

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SELECT DATE_FORMAT(CURDATE(),GET_FORMAT(DATE,'USA'))
FROM DUAL;

4.流程控制函数

4.1 IF(VALUE,VALUE1,VALUE2)

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SELECT last_name,salary,IF(salary >= 6000,'高工资','低工资') "details"
FROM employees;

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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

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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

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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;

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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

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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

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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。

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SELECT MD5('mysql'),SHA('mysql'),MD5(MD5('mysql'))
FROM DUAL;

ENCODE()\DECODE() 在mysql8.0中弃用。

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

6. MySQL信息函数

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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

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SELECT FORMAT(123.125,2),FORMAT(123.125,0),FORMAT(123.125,-2)
FROM DUAL;

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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。

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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

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SELECT BENCHMARK(100000,MD5('mysql'))
FROM DUAL;

CONVERT():可以实现字符集的转换

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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)

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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）

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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）

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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

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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

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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

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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

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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

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SELECT CONCAT(last_name,' earns ',salary,' monthly but wants ',TRUNCATE(salary*3,0)) "Dream Salary"
from employees;

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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;