# 第07章_单行函数

# 1. 数值函数
#基本的操作
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;

#取随机数
SELECT RAND(),RAND(),RAND(10),RAND(10),RAND(-1),RAND(-1)
FROM DUAL;

#四舍五入，截断操作
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;

SELECT TRUNCATE(123.456,0),TRUNCATE(123.496,1),TRUNCATE(129.45,-1)
FROM dual;

#单行函数可以嵌套
SELECT TRUNCATE(ROUND(123.456,2),0)
FROM dual;

#角度与弧度的互换
SELECT RADIANS(30),RADIANS(45),RADIANS(60),RADIANS(90),
       DEGREES(2*PI()),DEGREES(RADIANS(60))
FROM dual;

# 三角函数
SELECT SIN(RADIANS(30)),DEGREES(ASIN(1)),TAN(RADIANS(45)),DEGREES(ATAN(1))
FROM dual;

#指数和对数
SELECT POW(2,5),POWER(2,4),EXP(2)
FROM dual;

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

#进制间的转换
SELECT BIN(10),HEX(10),OCT(10),CONV(10,10,8)
FROM dual;

# 2. 字符串函数

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

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

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

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

SELECT UPPER('Hello'),LOWER('Hello')
FROM dual;

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

SELECT LEFT('hello',2),RIGHT('hello',3),RIGHT('hello',13)
FROM dual;

#LPAD: 实现右对齐效果
#RPAD: 实现左对齐效果
SELECT employee_id,last_name,LPAD(salary,10,' ')
FROM employees;

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

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

SELECT SUBSTR('hello',2,2),LOCATE('1ll','hello')
FROM dual;

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;

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

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

# 3.2 日期与时间戳的转换
SELECT UNIX_TIMESTAMP(),UNIX_TIMESTAMP('2021-10-01 12:12:32'),
       FROM_UNIXTIME(1667806653),FROM_UNIXTIME(1633061552)
FROM dual;
# 3.3 获取月份、星期、星期数、天数等函数
SELECT YEAR(CURDATE()),MONTH(CURDATE()),DAY(CURDATE()),
HOUR(CURTIME()),MINUTE(NOW()),SECOND(SYSDATE())
FROM DUAL;

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

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
SELECT TIME_TO_SEC(CURTIME()),
       SEC_TO_TIME(57332)
FROM dual;

#3.6 计算日期和时间的函数

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

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;

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()),12),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示格式化和解析

#之前，我们接触过隐式的格式化或解析

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

#格式化：
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
SELECT STR_TO_DATE('2022-November-7th 04:48:04 Monday 1','%Y-%M-%D %h:%i:%S %W %w')
FROM dual;

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

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

# 流程控制函数
# 4.1 IF(VALUE,VALUE1,VALUE2)

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

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
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
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;

# 4.4 CASE ... WHEN ... THEN ... WHEN ... THEN ... ELSE ...

/*

 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 1.3 倍数。

 */
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。

 */
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。
SELECT MD5('mysql'),SHA('mysql'),MD5(MD5('mysql'))
FROM dual;

#ENCODE() \ DECODE() 在mysql8.0中弃用。
/*
 SELECT ENCODE('qaqaq','mysql'),DECODE(ENCODE('qaqaq','mysql'),'mysql')
 FROM dual;
 */

# 6. MySQL信息函数
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
SELECT FORMAT(123.125,2),FORMAT(123.125,0),FORMAT(123.125,-2)
FROM dual;

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。
SELECT INET_ATON('192.168.1.100'),INET_NTOA(3232235876)
FROM dual;

#BENCHMARK() 用于测试表达式的执行时间
SELECT BENCHMARK(100000,MD5('mysql'))
FROM dual;
#CONVERT():可以实现字符集的转换
SELECT CHARSET('atguigu'),CHARSET(CONVERT('atguigu' USING 'utf8mb3'))
FROM dual;

数值，字符串重点

日期和时间重点