MySQL - function

function

One 、 The function classification ：

1. One line function ： One input one output
   （1） Manipulate data objects
   （2） Accept parameters and return a result
   （3） Change only one line
   （4） Each line returns a result
   （5） Can be nested
   （6） The parameter can be a column or a value
2. Multiline functions

Basic functions

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)
FROM DUAL;

#  When you pass in the same factor , The random numbers returned are the same , This explanation `RAND()` The bottom layer of a function is actually a random number calculated from a factor , It's a pseudo-random number 
SELECT RAND(),RAND(),RAND(10),RAND(10),RAND(-1),RAND(-1)
FROM DUAL;

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;

#  Single line functions can be nested 
SELECT TRUNCATE(ROUND(123.456,2),0)
FROM DUAL;

Angle and radian exchange function

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

Trigonometric functions

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

Exponents and logarithms

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

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

Conversion between bases

CONV(x,f1,f2) take f1 It's binary x convert to f2 Base number , Such as CONV(10,2,8) Is to convert binary 10 Convert to octal , The binary 10 That is to say 2, Conversion to octal is also 2

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

String function

SELECT ASCII('Abcdfsf'),CHAR_LENGTH('hello'),CHAR_LENGTH(' We '),
LENGTH('hello'),LENGTH(' We ')

LENGTH('hello') One character is stored in one byte , therefore LENGTH('hello') standing 5 Bytes . and UTF-8 Each Chinese character accounts for 3 Bytes , therefore LENGTH(' We ') Occupy 6 Bytes . use LENGTH() This is how many bytes are used to measure the underlying storage ,CHAR_LENGTH() It measures how many characters are in the memory , therefore CHAR_LENGTH('hello'),CHAR_LENGTH(' We ') All for 5.

#  String concatenation ：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;

String and string are spliced with the first parameter

If the first argument is an empty string

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

The effect is the same as CONCAT Method ：

SELECT CONCAT('hello','world','hello','beijing')
FROM DUAL;

SELECT INSERT('helloworld',2,3,'aaaaa'),REPLACE('hello','ll','mmm')
FROM DUAL;

The index of the string is from 1 At the beginning ,INSERT('helloworld',2,3,'aaaaa') take helloworld In the Chinese Index 2 Start , Count back 3 Characters （ Including 3 Characters ）, Put these characters （ Characters in this range ） Replace with aaaaa.REPLACE('hello','ll','mmm') take hello Medium ll Replace with mmm

SELECT REPLACE('hello','lol','mmm')
FROM DUAL;

If in the future hello Not found in lol, No replacement, no processing, no error reporting , Returns the original string .

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

stay Oracle String is case sensitive , The following code will only find last_name = 'King'; People who ,king and KING Can't find

SELECT last_name,salary
FROM employees
WHERE last_name = 'King';

So you can use UPPER()、LOWER() Change my ：

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

however MySQL There is no such problem in ,MySQL The string is not case sensitive

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

# LPAD: Achieve the right alignment effect 
# RPAD: Achieve left alignment effect 
SELECT employee_id,last_name,LPAD(salary,10,'*')
FROM employees;

LPAD(salary,10,'*') Express salary Occupy 10 position （ The decimal point also counts ）, Not enough * stay On the left A filling

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

TRIM( character string ) Used to remove spaces at the beginning and end of a string ,TRIM('oo' FROM 'ooheollo') Used to remove ooheollo Head and tail oo,LTRIM()、RTRIM() Respectively used to remove the first 、 Trailing space

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

SPACE() Used to provide spaces ,STRCMP() Used for string ratio size , return 1 Indicates that the previous string is larger than the following one

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

SUBSTR( character string , Index position （ Intercept starting position , To intercept the character at this position ）, The number of intercepts )
LOCATE() Where the first string first appears in the second string

If there is no first string in the second string , return 0

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;

NULLIF( character string 1, character string 2) Compare two strings , If equal , Then return to NULL, Otherwise, return the string 1

Date and time functions

Get date 、 Time

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

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

Date and time stamp conversion

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

Get month 、 week 、 Weeks 、 Functions such as days

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;

Operation function of date

type The value and meaning of ：

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

Time and second conversion function

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

A function that calculates the date and time

type The value of ：

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

DATE_ADD(NOW(),INTERVAL 1 YEAR), Add... At the current time 1 year ,DATE_ADD(NOW(),INTERVAL -1 YEAR) amount to DATE_SUB(NOW(),INTERVAL 1 YEAR) Both are subtracted at the current time 1 year

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, # It could be negative 
DATE_ADD(NOW(), INTERVAL '1_1' YEAR_MONTH) AS col6 # Need single quotes 
FROM DUAL;

DATE_ADD('2021-10-21 23:32:12',INTERVAL '1_1' MINUTE_SECOND) stay 2021-10-21 23:32:12 To add 1 branch 1 second , Be careful '1_1' Not numerical , Use '' Lead up

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;

SUBTIME(NOW(),'1:1:3') Subtract... From the current time 1 Hours 1 minute 1 second

Formatting and parsing of dates

Above Not GET_FORMAT function in fmt Common format characters and descriptions of parameters are as follows ：

GET_FORMAT function in date_type and format_type The parameter values are as follows ：


format ： date —> character string
analysis ： character string ----> date
At this point, we are talking about the explicit formatting and parsing of dates , Before , We've been exposed to implicit formatting or parsing

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

Here '1993-01-13' It's a string , Because it satisfies Date Format , So when searching , The bottom layer will automatically convert this string to Date Format , This is implicit formatting or parsing

# format ：
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;

# analysis ： The reverse of formatting 
SELECT STR_TO_DATE('2021-October-25th 11:37:30 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;

Process control functions

Process processing functions can be based on different conditions , Perform different processes , Can be in SQL Statement to implement different conditional choices .MySQL The process processing functions in mainly include IF()、IFNULL() and CASE() function .

#4.1 IF(VALUE,VALUE1,VALUE2)
SELECT last_name,salary,IF(salary >= 6000,' High wages ',' Low wages ') "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): As a IF(VALUE,VALUE1,VALUE2) In special circumstances 
SELECT last_name,commission_pct,IFNULL(commission_pct,0) "details"
FROM employees;

#4.3 CASE WHEN ... THEN ...WHEN ... THEN ... ELSE ... END
#  Be similar to java Of if ... else if ... else if ... else
SELECT last_name,salary,CASE WHEN salary >= 15000 THEN ' Bones jing ' 
			     WHEN salary >= 10000 THEN ' potential share '
			     WHEN salary >= 8000 THEN ' Little loser '
			     ELSE ' grassroots ' END "details",department_id
FROM employees;

SELECT last_name,salary,CASE WHEN salary >= 15000 THEN ' Bones jing ' 
			     WHEN salary >= 10000 THEN ' potential share '
			     WHEN salary >= 8000 THEN ' Little loser '
			     END "details"
FROM employees;

#4.4 CASE ... WHEN ... THEN ... WHEN ... THEN ... ELSE ... END
#  Be similar to java Of swich ... case...
/*  practice 1  The inquiry department number is  10,20, 30  Employee information ,  If the department number is  10,  Print their salary  1.1  times , 20  Department No ,  Print their salary  1.2  times , 30  Department No , Print their salary  1.3  Multiple ,  Other departments , Print their salary  1.4  Multiple  */
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;

/*  practice 2  The inquiry department number is  10,20, 30  Employee information ,  If the department number is  10,  Print their salary  1.1  times , 20  Department No ,  Print their salary  1.2  times , 30  Department No. prints its salary  1.3  Multiple  */
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);

Encryption and decryption functions

The encryption and decryption function is mainly used to encrypt and decrypt the data in the database , To prevent data from being stolen by others .

# PASSWORD() stay mysql8.0 To discard .
SELECT MD5('mysql'),SHA('mysql'),MD5(MD5('mysql'))
FROM DUAL;

MD5() and SHA() These two encryption methods are irreversible , Only plain text can be encrypted into dark text , You cannot decrypt dark text into plain text