MySQL function

summary

stay MySQL in , In order to improve code reusability and hide implementation details ,MySQL Many functions are provided , Function can be understood as someone else's closed template code .

stay MySQL in , There are many functions , The main categories are ：

－ Aggregate functions

－ Mathematical functions

－ String function

－ Date function

－ Control flow function

－ Window function

Aggregate functions

count , sum, min, max, avg These are aggregate functions .

group_concat

group_concat() Function first according to group by The specified columns are grouped , And separate... With a separator , And connect with the values in the same group , Returns a string .

Format ：

group_concat( [distinct]  Field name  [order by  Sort field  asc/desc] [separator ' Separator '] )

explain ： use distinct You can exclude duplicate values , If you need to sort the values in the results , have access to order by Clause ,separator Is a string , Default to comma .

Example ：

use mydb1;
create table emp(
    emp_id int primary key auto_increment comment ' Number ',
    emp_name char(20) not null default '' comment ' full name ',
    salary decimal(10,2) not null default 0 comment ' Wages ',
    department char(20) not null default '' comment ' department '
 );
 
 insert into emp( emp_name, salary, department)
	values (' Zhang Fei ', 5000, ' Shu Kingdom '),
	 (' zhaoyun ', 8000, ' Shu Kingdom '),
	 (' Guan Yunchang ', 10000, ' Shu Kingdom '),
	 (' Liu bei ', 25000, ' Shu Kingdom '),
	 (' king of Wu in the Three Kingdoms Era ', 25000, ' Wu kingdom '),
	 (' Sun shangxiang ', 15000, ' Wu kingdom '),
	 (' Liu chan ', 5000, ' Shu Kingdom '),
	 (' Sima ', 15000, ' State of Wei '),
	 (' Cao Cao ', 25000, ' State of Wei '),
	 (' Cao Pi ', 25000, ' State of Wei '),
	 (' Lyu3 bu4 ', 35000, ' A group of Heroes ');

--  Merge all names into one line 
select group_concat(emp_name) from emp;
--  Zhang Fei , zhaoyun , Guan Yunchang , Liu bei , king of Wu in the Three Kingdoms Era , Sun shangxiang , Liu chan , Sima , Cao Cao , Cao Pi , Lyu3 bu4 
select group_concat(emp_name SEPARATOR '、') from emp;

--  Specify sorting method and separator 
select department, group_concat(emp_name ) from emp group by department;
select department, group_concat(emp_name order by salary desc) from emp group by department;

Mathematical functions

Function name	describe	Example
ABS(x)	return x The absolute value of	SELECT ABS(-1) – return 1
ACOS(x)	seek x The arccosine of （ In radians ）,x Is a numerical value	SELECT ACOS(0.25);
ASIN(x)	Find the inverse sine （ In radians ）,x Is a numerical value	SELECT ASIN(0.25);
ATAN(x)	Find the arctangent （ In radians ）,x Is a numerical value	SELECT ATAN(2.5);
ATAN2(n, m)	Find the arctangent （ In radians ）	SELECT ATAN2(-0.8, 2);
AVG(expression)	Returns the average value of an expression ,expression It's a field	return Products In the table Price The average value of the field ：SELECT AVG(Price) AS AveragePrice FROM Products;
CEIL(x)	Returns greater than or equal to x Minimum integer of	SELECT CEIL(1.5) -- return 2
CEILING(x)	Returns greater than or equal to x Minimum integer of	SELECT CEILING(1.5); -- return 2
COS(x)	Find the cosine ( The parameter is radian )	SELECT COS(2);
COT(x)	Find the cotangent value ( The parameter is radian )	SELECT COT(6);
COUNT(expression)	Returns the total number of records queried ,expression A parameter is a field or * Number	return Products In the table products How many records are there in the field ：SELECT COUNT(ProductID) AS NumberOfProducts FROM Products;
DEGREES(x)	Convert radians to degrees	SELECT DEGREES(3.1415926535898) -- 180
n DIV m	to be divisible by ,n For divisor ,m Divisor	Calculation 10 Except in 5：SELECT 10 DIV 5; -- 2
EXP(x)	return e Of x Power	Calculation e The third power of ：SELECT EXP(3) -- 20.085536923188
FLOOR(x)	Returns less than or equal to x Maximum integer for	Less than or equal to 1.5 The integer of ：SELECT FLOOR(1.5) -- return 1
GREATEST(expr1, expr2, expr3, …)	Returns the maximum value in the list	Returns the maximum value in the following list of numbers ：SELECT GREATEST(3, 12, 34, 8, 25); -- 34 Returns the maximum value in the following string list ：SELECT GREATEST("Google", "Runoob", "Apple"); -- Runoob
LEAST(expr1, expr2, expr3, …)	Returns the minimum value in the list	Returns the minimum value in the following list of numbers ：SELECT LEAST(3, 12, 34, 8, 25); -- 3 Returns the minimum value in the following string list ：SELECT LEAST("Google", "Runoob", "Apple"); -- Apple
LN	Returns the natural logarithm of a number , With e Bottom .	return 2 The natural logarithm of ：SELECT LN(2); -- 0.6931471805599453
LOG(x) or LOG(base, x)	Return to the natural logarithm ( With e Log base ), If a base Parameters , be base Specifies the base number for the .	SELECT LOG(20.085536923188) -- 3 SELECT LOG(2, 4); -- 2
LOG10(x)	Return to 10 Log base	SELECT LOG10(100) -- 2
LOG2(x)	Return to 2 Log base	Return to 2 Bottom 6 The logarithmic ：SELECT LOG2(6); -- 2.584962500721156
MAX(expression)	Return field expression Maximum of	Return to the data table Products Middle field Price The maximum of ：SELECT MAX(Price) AS LargestPrice FROM Products;
MIN(expression)	Return field expression Minimum of	Return to the data table Products Middle field Price The minimum value of ：SELECT MIN(Price) AS MinPrice FROM Products;
MOD(x,y)	return x Divide y The remainder after	5 Except in 2 The remainder of ：SELECT MOD(5,2) -- 1
PI()	Return the PI (3.141593）	SELECT PI() --3.141593
POW(x,y)	return x Of y Power	2 Of 3 Power ：SELECT POW(2,3) -- 8
POWER(x,y)	return x Of y Power	2 Of 3 Power ：SELECT POWER(2,3) -- 8
RADIANS(x)	Convert the Angle to radians	180 Degrees to radians ：SELECT RADIANS(180) -- 3.1415926535898
RAND()	return 0 To 1 The random number	SELECT RAND() --0.93099315644334
ROUND(x)	Return from x The nearest integer	SELECT ROUND(1.23456) --1
SIGN(x)	return x The symbol of ,x It's a negative number 、0、 Positive numbers return respectively -1、0 and 1	SELECT SIGN(-10) -- (-1)
SIN(x)	Find the sine ( The parameter is radian )	SELECT SIN(RADIANS(30)) -- 0.5
SQRT(x)	return x The square root of	25 The square root of ：SELECT SQRT(25) -- 5
SUM(expression)	Returns the sum of the specified fields	Calculation OrderDetails Fields in the table Quantity The sum of ：SELECT SUM(Quantity) AS TotalItemsOrdered FROM OrderDetails;
TAN(x)	Find tangent ( The parameter is radian )	SELECT TAN(1.75); -- -5.52037992250933
TRUNCATE(x,y)	Returns the value x Keep it after the decimal point y The value of a （ And ROUND The biggest difference is that there is no rounding ）	SELECT TRUNCATE(1.23456,3) -- 1.234

String function

function	describe	example
ASCII(s)	Return string s Of the first character of ASCII code .	return CustomerName The first letter of the field ASCII code ：SELECT ASCII(CustomerName) AS NumCodeOfFirstChar FROM Customers;
CHAR_LENGTH(s)	Return string s The number of characters	Return string RUNOOB The number of characters SELECT CHAR_LENGTH("RUNOOB") AS LengthOfString;
CHARACTER_LENGTH(s)	Return string s The number of characters	Return string RUNOOB The number of characters SELECT CHARACTER_LENGTH("RUNOOB") AS LengthOfString;
CONCAT(s1,s2…sn)	character string s1,s2 When multiple strings are merged into a single string	Merge multiple strings SELECT CONCAT("SQL ", "Runoob ", "Gooogle ", "Facebook") AS ConcatenatedString;
CONCAT_WS(x, s1,s2…sn)	Same as CONCAT(s1,s2,…) function , But add... Between each string x,x It can be a separator	Merge multiple strings , And add a separator ：SELECT CONCAT_WS("-", "SQL", "Tutorial", "is", "fun!")AS ConcatenatedString;
FIELD(s,s1,s2…)	Returns the first string s In the string list (s1,s2…) Position in	Return string c Position in the list value ：SELECT FIELD("c", "a", "b", "c", "d", "e");
FIND_IN_SET(s1,s2)	Return in string s2 China and s1 The location of the matching string	Return string c Position in the specified string ：SELECT FIND_IN_SET("c", "a,b,c,d,e");
FORMAT(x,n)	The function can change the number to x format “#,###.##”, take x Keep it after the decimal point n position , Round the last one .	Formatting Numbers “#,###.##” form ：SELECT FORMAT(250500.5634, 2); -- Output 250,500.56
INSERT(s1,x,len,s2)	character string s2 Replace s1 Of x The starting length of the position is len String	Starting from the first position of the string 6 Replace characters with runoob：SELECT INSERT("google.com", 1, 6, "runoob"); -- Output ：runoob.com
LOCATE(s1,s)	From a string s In order to get s1 The beginning of	obtain b In string abc Position in ：SELECT LOCATE('st','myteststring'); -- 5 Return string abc in b The location of ：SELECT LOCATE('b', 'abc') -- 2
LCASE(s)	The string s All of the letters of the are changed into lower case letters	character string RUNOOB Convert to lowercase ：SELECT LCASE('RUNOOB') -- runoob
LEFT(s,n)	Return string s Before n Characters	Return string runoob The first two characters in ：SELECT LEFT('runoob',2) -- ru
LOWER(s)	The string s All of the letters of the are changed into lower case letters	character string RUNOOB Convert to lowercase ：SELECT LOWER('RUNOOB') -- runoob
LPAD(s1,len,s2)	In string s1 Start with a string s2, Make the string length to len	The string xx Fill in abc The beginning of the string ：SELECT LPAD('abc',5,'xx') -- xxabc
LTRIM(s)	Remove string s The space at the beginning	Remove string RUNOOB The space at the beginning ：SELECT LTRIM(" RUNOOB") AS LeftTrimmedString;-- RUNOOB
MID(s,n,len)	From a string s Of n The position intercept length is len Substring of , Same as SUBSTRING(s,n,len)	From a string RUNOOB No 2 Location intercepts 3 individual character ：SELECT MID("RUNOOB", 2, 3) AS ExtractString; -- UNO
POSITION(s1 IN s)	From a string s In order to get s1 The beginning of	Return string abc in b The location of ：SELECT POSITION('b' in 'abc') -- 2
REPEAT(s,n)	The string s repeat n Time	The string runoob Repeat three times ：SELECT REPEAT('runoob',3) -- runoobrunoobrunoob
REPLACE(s,s1,s2)	The string s2 Alternative string s String in s1	The string abc The characters in a Replace with characters x：SELECT REPLACE('abc','a','x') --xbc
REVERSE(s)	The string s In reverse order	The string abc In reverse order ：SELECT REVERSE('abc') -- cba
RIGHT(s,n)	Return string s After n Characters	Return string runoob The last two characters of ：SELECT RIGHT('runoob',2) -- ob
RPAD(s1,len,s2)	In string s1 Add a string at the end of s2, Make the length of the string equal to len	The string xx Fill in abc At the end of the string ：SELECT RPAD('abc',5,'xx') -- abcxx
RTRIM(s)	Remove string s Space at the end	Remove string RUNOOB Space at the end of ：SELECT RTRIM("RUNOOB ") AS RightTrimmedString; -- RUNOOB
SPACE(n)	return n A space	return 10 A space ：SELECT SPACE(10);
STRCMP(s1,s2)	Compare strings s1 and s2, If s1 And s2 Equal return 0 , If s1>s2 return 1, If s1<s2 return -1	Compare strings ：SELECT STRCMP("runoob", "runoob"); -- 0
SUBSTR(s, start, length)	From a string s Of start The position intercept length is length Substring of	From a string RUNOOB No 2 Location intercepts 3 individual character ：SELECT SUBSTR("RUNOOB", 2, 3) AS ExtractString; -- UNO
SUBSTRING(s, start, length)	From a string s Of start The position intercept length is length Substring of	From a string RUNOOB No 2 Location intercepts 3 individual character ：SELECT SUBSTRING("RUNOOB", 2, 3) AS ExtractString; -- UNO
SUBSTRING_INDEX(s, delimiter, number)	Return from string s Of the number Separators that appear delimiter After the string . If number Positive number , Back to page number The string to the left of characters . If number It's a negative number , Back to page (number The absolute value of ( Count from the right )) The string to the right of characters .	SELECT SUBSTRING_INDEX('a*b','*',1) -- a SELECT SUBSTRING_INDEX('a*b','*',-1) -- b SELECT SUBSTRING_INDEX(SUBSTRING_INDEX('a*b*c*d*e','*',3),'*',-1) -- c
TRIM(s)	Remove string s The spaces at the beginning and the end	Remove string RUNOOB The leading and trailing spaces of ：SELECT TRIM(' RUNOOB ') AS TrimmedString;
UCASE(s)	Convert strings to uppercase	The string runoob Convert to uppercase ：SELECT UCASE("runoob"); -- RUNOOB
UPPER(s)	Convert strings to uppercase	The string runoob Convert to uppercase ：SELECT UPPER("runoob"); -- RUNOOB

Date function

function	describe	example
ADDDATE(d,n)	Calculate start date d add n The date of day	SELECT ADDDATE("2017-06-15", INTERVAL 10 DAY); ->2017-06-25
ADDTIME(t,n)	n It's a time expression , Time t Add the time expression n	Add 5 second ：SELECT ADDTIME('2011-11-11 11:11:11', 5); ->2011-11-11 11:11:16 ( second ) add to 2 Hours , 10 minute , 5 second :SELECT ADDTIME("2020-06-15 09:34:21", "2:10:5"); -> 2020-06-15 11:44:26
CURDATE()	Return current date	SELECT CURDATE(); -> 2018-09-19
CURRENT_DATE()	Return current date	SELECT CURRENT_DATE(); -> 2018-09-19
CURRENT_TIME	Return current time	SELECT CURRENT_TIME(); -> 19:59:02
CURRENT_TIMESTAMP()	Returns the current date and time	SELECT CURRENT_TIMESTAMP() -> 2018-09-19 20:57:43
CURTIME()	Return current time	SELECT CURTIME(); -> 19:59:02
DATE()	Extract a date value from a date or datetime expression	SELECT DATE("2017-06-15"); -> 2017-06-15
DATEDIFF(d1,d2)	Calculate the date d1->d2 The days between	SELECT DATEDIFF('2001-01-01','2001-02-02') -> -32
DATE_ADD(d,INTERVAL expr type)	Calculate start date d Add the date after a period of time	SELECT DATE_ADD("2017-06-15", INTERVAL 10 DAY); -> 2017-06-25 SELECT DATE_ADD("2017-06-15 09:34:21", INTERVAL 15 MINUTE); -> 2017-06-15 09:49:21 SELECT DATE_ADD("2017-06-15 09:34:21", INTERVAL -3 HOUR); ->2017-06-15 06:34:21 SELECT DATE_ADD("2017-06-15 09:34:21", INTERVAL -3 MONTH); ->2017-04-15
DATE_FORMAT(d,f)	By expression f To display the date d	SELECT DATE_FORMAT('2011-11-11 11:11:11','%Y-%m-%d %r') -> 2011-11-11 11:11:11 AM
DATE_SUB(date,INTERVAL expr type)	Function to subtract a specified time interval from a date .	Orders In the table OrderDate Field subtraction 2 God ：SELECT OrderId,DATE_SUB(OrderDate,INTERVAL 2 DAY) AS OrderPayDate FROM Orders
DAY(d)	Returns the date value d The date part of	SELECT DAY("2017-06-15"); -> 15
DAYNAME(d)	Return date d What day is , Such as Monday,Tuesday	SELECT DAYNAME('2011-11-11 11:11:11') ->Friday
DAYOFMONTH(d)	Calculate the date d It's the day of the month	SELECT DAYOFMONTH('2011-11-11 11:11:11') ->11
DAYOFWEEK(d)	date d What day is today ,1 Sunday ,2 Monday , And so on	SELECT DAYOFWEEK('2011-11-11 11:11:11') ->6
DAYOFYEAR(d)	Calculate the date d It's the day of the year	SELECT DAYOFYEAR('2011-11-11 11:11:11') ->315
EXTRACT(type FROM d)	From the date d Get the specified value from the ,type Specifies the value to be returned . t	SELECT EXTRACT(MINUTE FROM '2011-11-11 11:11:11') -> 11
FROM_DAYS(n)	Calculate from 0000 year 1 month 1 The day begins n Days after	SELECT FROM_DAYS(1111) -> 0003-01-16
HOUR(t)	return t The hour value in	SELECT HOUR('1:2:3') -> 1
LAST_DAY(d)	Returns the last day of the month for a given date	SELECT LAST_DAY("2017-06-20"); -> 2017-06-30
LOCALTIME()	Returns the current date and time	SELECT LOCALTIME() -> 2018-09-19 20:57:43
LOCALTIMESTAMP()	Returns the current date and time	SELECT LOCALTIMESTAMP() -> 2018-09-19 20:57:43
MAKEDATE(year, day-of-year)	Based on the given parameter year year And the number of days in the year day-of-year Return a date	SELECT MAKEDATE(2017, 3); -> 2017-01-03
MAKETIME(hour, minute, second)	Combination time , The parameters are hour 、 minute 、 second	SELECT MAKETIME(11, 35, 4); -> 11:35:04
MICROSECOND(date)	Returns the number of microseconds corresponding to the date parameter	SELECT MICROSECOND("2017-06-20 09:34:00.000023"); -> 23
MINUTE(t)	return t Minutes in	SELECT MINUTE('1:2:3') -> 2
MONTHNAME(d)	Returns the name of the month in the date , Such as November	SELECT MONTHNAME('2011-11-11 11:11:11') -> November
MONTH(d)	Return date d The month in is worth ,1 To 12	SELECT MONTH('2011-11-11 11:11:11') ->11
NOW()	Returns the current date and time	SELECT NOW() -> 2018-09-19 20:57:43
PERIOD_ADD(period, number)	by year - month Add a period to the combined date	SELECT PERIOD_ADD(201703, 5); -> 201708
PERIOD_DIFF(period1, period2)	Returns the month difference between two periods	SELECT PERIOD_DIFF(201710, 201703); -> 7
QUARTER(d)	Return date d What season is it , return 1 To 4	SELECT QUARTER('2011-11-11 11:11:11') -> 4
SECOND(t)	return t The second value in	SELECT SECOND('1:2:3') -> 3
SEC_TO_TIME(s)	Time in seconds s Convert to minutes and seconds	SELECT SEC_TO_TIME(4320) -> 01:12:00
STR_TO_DATE(string, format_mask)	Convert string to date	SELECT STR_TO_DATE("August 10 2017", "%M %d %Y"); -> 2017-08-10
SUBDATE(d,n)	date d subtract n Days after	SELECT SUBDATE('2011-11-11 11:11:11', 1) ->2011-11-10 11:11:11 ( The default is days )
SUBTIME(t,n)	Time t subtract n The second time	SELECT SUBTIME('2011-11-11 11:11:11', 5) ->2011-11-11 11:11:06 ( second )
SYSDATE()	Returns the current date and time	SELECT SYSDATE() -> 2018-09-19 20:57:43
TIME(expression)	Extract the time part of the incoming expression	SELECT TIME("19:30:10"); -> 19:30:10
TIME_FORMAT(t,f)	By expression f The request shows the time t	SELECT TIME_FORMAT('11:11:11','%r') 11:11:11 AM
TIME_TO_SEC(t)	Time t Convert to seconds	SELECT TIME_TO_SEC('1:12:00') -> 4320
TIMEDIFF(time1, time2)	Calculate time difference	mysql> SELECT TIMEDIFF("13:10:11", "13:10:10"); -> 00:00:01 mysql> SELECT TIMEDIFF('2000:01:01 00:00:00', -> '2000:01:01 00:00:00.000001'); -> '-00:00:00.000001' mysql> SELECT TIMEDIFF('2008-12-31 23:59:59.000001', -> '2008-12-30 01:01:01.000002'); -> '46:58:57.999999'
TIMESTAMP(expression, interval)	When a single parameter , Function returns a date or datetime expression ; Yes 2 When the parameters , Add parameters to	mysql> SELECT TIMESTAMP("2017-07-23", "13:10:11"); -> 2017-07-23 13:10:11 mysql> SELECT TIMESTAMP('2003-12-31'); -> '2003-12-31 00:00:00' mysql> SELECT TIMESTAMP('2003-12-31 12:00:00','12:00:00'); -> '2004-01-01 00:00:00'
TIMESTAMPDIFF(unit,datetime_expr1,datetime_expr2)	Calculate the time difference , return datetime_expr2 − datetime_expr1 The time difference	mysql> SELECT TIMESTAMPDIFF(DAY,'2003-02-01','2003-05-01'); // Calculate the number of days between the two times -> 89 mysql> SELECT TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01'); // Calculate the number of months between the two times -> 3 mysql> SELECT TIMESTAMPDIFF(YEAR,'2002-05-01','2001-01-01'); // Calculate the number of years between the two times -> -1 mysql> SELECT TIMESTAMPDIFF(MINUTE,'2003-02-01','2003-05-01 12:05:55'); // Calculate the number of minutes between the two times -> 128885
TO_DAYS(d)	Calculate the date d distance 0000 year 1 month 1 Days of the day	SELECT TO_DAYS('0001-01-01 01:01:01') -> 366
WEEK(d)	Calculate the date d It's the first few weeks of the year , The scope is 0 To 53	SELECT WEEK('2011-11-11 11:11:11') -> 45
WEEKDAY(d)	date d What day is ,0 For Monday ,1 For Tuesday	SELECT WEEKDAY("2017-06-15"); -> 3
WEEKOFYEAR(d)	Calculate the date d It's the first few weeks of the year , The scope is 0 To 53	SELECT WEEKOFYEAR('2011-11-11 11:11:11') -> 45

Demo example ：

--  Date function 

--  Get the timestamp 
select UNIX_TIMESTAMP()

--  Convert a string to a millisecond value  
select UNIX_TIMESTAMP('2022-01-19 18:21:00')

--  Converts the time in milliseconds to a date in the specified format 
select from_unixtime('1642587660', '%Y-%m-%d %H-%i-%s')\

--  Get the current date 
select curdate()
select current_date()

--  Get the current time, minute, second 
select current_time()

--  Gets the minutes and seconds of the year, month and day 
select current_timestamp()

--  Get the date from the date string 
select date('2021-12-11 12:12:12')

-- Calculate the time interval 
select datediff('2021-01-11', '2022-12-12');

-- Calculate time difference 
select timediff('2021-12-11 12:12:12', '2021-2-11 12:12:12');
select timediff('12:12:12', '11:12:12');


--  Convert string to date 
select STR_TO_DATE('2021-12-11 12:12:12','%Y-%m-%D %H:%i:%s');

--  Subtract the date , The date jumps forward 
select date_sub('2021-3-01', interval 2 day);
select date_sub('2021-3-2', interval 2 month);

--  Add the date , The date jumps to the right 
select date_add('2021-02-1' ,interval 2 month);
select date_add('2021-02-1', interval 2 day);

--  Get the time from the date  [ hour, month, day, hour]
select extract(hour from '2021-01-22 12:01:00');
select extract(year from '2021-01-22 12:01:00');
select extract(month from '2021-01-22 12:01:00');

--  Get the last day of a given date 
select last_day('2021-12-01'); -- 2021-12-31


--  Gets the date of the year and the specified number of days 
select makedate('2022', 53); -- 2022 In the first 53 God 

--  Obtain the time, minute and second of month, day and year according to the date 
select year('2021-01-22 12:01:00')
select month('2021-01-22 12:01:00')
select day('2021-01-22 12:01:00')
select minute('2021-01-22 12:01:00')
select QUARTER('2021-01-22 12:01:00') --  quarter 

--  Get information based on date 
select DAYOFMONTH('2022-01-18 18:13:00') --  The day of the month 
select DAYOFWEEK('2022-01-18 18:13:00')  --  What day 
select DAYOFYEAR('2022-01-18 18:13:00')  --  Get the day of the year 

--  week 
select WEEK('2022-01-18') --  The first few weeks of the year 
select WEEKDAY('2022-01-18') --  The acquisition date is the day of the week ,0 For weeks 1,1 For weeks 2
select WEEKOFYEAR('2022-01-18') --  The calculation date is the week ordinal of the year ,0-53
select YEARWEEK('2022-01-18') --  Return year and week  202203,2022 In the first 3 Zhou 
select NOW() --  Returns the current date and time 

MySQL Advanced functions

function	describe	example
BIN(x)	return x Binary code of	15 Of 2 Hexadecimal code :SELECT BIN(15); -- 1111
BINARY(s)	The string s Convert to binary string	SELECT BINARY "RUNOOB"; -> RUNOOB
CASE expression WHEN condition1 THEN result1 WHEN condition2 THEN result2 ... WHEN conditionN THEN resultN ELSE result END	CASE Represents the beginning of a function ,END End of function . If condition1 establish , Then return to result1, If condition2 establish , Then return to result2, When all fail, return to result, And when one is established , The latter will not be implemented .	SELECT CASE 　WHEN 1 > 0 　THEN '1 > 0' 　WHEN 2 > 0 　THEN '2 > 0' 　ELSE '3 > 0' 　END ->1 > 0
CAST(x AS type)	Convert data type	Convert string date to date ：SELECT CAST("2017-08-29" AS DATE); -> 2017-08-29
COALESCE(expr1, expr2, …, expr_n)	Returns the first non empty expression in the parameter （ From left to right ）	SELECT COALESCE(NULL, NULL, NULL, 'runoob.com', NULL, 'google.com'); -> runoob.com
CONNECTION_ID()	Returns a unique connection ID	SELECT CONNECTION_ID(); -> 4292835
CONV(x,f1,f2)	return f1 The base number becomes f2 Hexadecimal number	SELECT CONV(15, 10, 2); -> 1111
CONVERT(s USING cs)	Function to string s The character set of becomes cs	SELECT CHARSET('ABC') ->utf-8 SELECT CHARSET(CONVERT('ABC' USING gbk)) ->gbk
CURRENT_USER()	Return to current user	SELECT CURRENT_USER(); -> [email protected]%
DATABASE()	Returns the current database name	SELECT DATABASE(); -> runoob
LAST_INSERT_ID()	Returns the most recently generated AUTO_INCREMENT value	SELECT LAST_INSERT_ID(); ->6
NULLIF(expr1, expr2)	Compare two strings , If the string expr1 And expr2 equal return NULL, Otherwise return to expr1	SELECT NULLIF(25, 25); ->
SESSION_USER()	Return to current user	SELECT SESSION_USER(); -> [email protected]%
SYSTEM_USER()	Return to current user	SELECT SYSTEM_USER(); -> [email protected]%
USER()	Return to current user	SELECT USER(); -> [email protected]%
VERSION()	Return the version number of the database	SELECT VERSION() -> 5.6.34

Control flow function

IF control

function	describe	Example
IF(expr,v1,v2)	If the expression expr establish , Return results v1; otherwise , Return results v2.	SELECT IF(1 > 0,' correct ',' error ') -> correct
IFNULL(v1,v2)	If v1 The value of the NULL, Then return to v1, Otherwise return to v2.	SELECT IFNULL(null,'Hello Word') ->Hello Word
ISNULL(expression)	Determine whether the expression is NULL	SELECT ISNULL(NULL); ->1

Sample code ：

-- IF Sentence judgment 
select *, if(salary >=25000, ' The Lord ', ' Senior general ') from emp;

case when end function

Format ：

CASE case_value
	WHEN when_value THEN
		statement_list
	ELSE
		statement_list
END;

The operation sample ：

--  Create order form 
create table orders(
	oid int primary key, 
	price double, 
	payType int -- 1 Wechat payment  2 Alipay  3 other 
);

use mydb1;
insert into orders values(1, 1200, 1);
insert into orders values(2, 1100, 2);
insert into orders values(3, 800, 3);
insert into orders values(4, 5200, 1);
insert into orders values(5, 100, 2);

--  Output payment method 
select 
	*, 
	CASE payType
		WHEN 1 THEN ' Wechat payment '
		WHEN 2 THEN ' Alipay '
		ELSE ' Other payments '
	END as payIntf
from orders;

Window function

Ordinal function

ROW_NUMBER(), RANK(), DENSE_RANK() Group sorting can be realized , And add serial number .

Format ：

row_number() | rank() | dense_rank() over(
	partition by ...
	order by ...
)

The operation sample ：

create table employee(
	dname varchar(20), --  Department name 
	eid varchar(20),
	ename varchar(20),
	hiredate date, --  Entry time 
	salary double --  Salary 
);

insert into employee values(' Shu Kingdom ', '1001', ' Liu bei ', '2021-11-01', 15000);
insert into employee values(' Shu Kingdom ', '1002', ' Guan yu ', '2021-11-02', 5000);
insert into employee values(' Shu Kingdom ', '1003', ' Zhang Fei ', '2021-11-03', 5000);
insert into employee values(' Shu Kingdom ', '1004', ' zhaoyun ', '2021-11-04', 7000);
insert into employee values(' Shu Kingdom ', '1005', ' d ', '2021-11-05', 4000);
insert into employee values(' Shu Kingdom ', '1006', ' Huang Zhong ', '2021-11-06', 4000);

insert into employee values(' State of Wei ', '1007', ' Cao Cao ', '2021-11-01', 15000);
insert into employee values(' State of Wei ', '1008', ' Xu Zhen ', '2021-11-01', 3000);
insert into employee values(' State of Wei ', '1009', ' Dianwei ', '2021-11-01', 3000);
insert into employee values(' State of Wei ', '1010', ' Zhang liao ', '2021-11-01', 5000);
insert into employee values(' State of Wei ', '1011', ' Summer ', '2021-11-01', 5000);
insert into employee values(' State of Wei ', '1012', ' Sima ', '2021-11-01', 8000);

 --  Sort the employees of each department according to their salary , And output the ranking 
 select 
	dname, ename, salary,
	row_number() over(partition by dname order by salary desc) as rn 
from employee;


--  Three sorting functions 
 select 
	dname, ename, salary,
	row_number() over(partition by dname order by salary desc) as rn,
	rank() over(partition by dname order by salary desc) as rn2,
	dense_rank() over(partition by dname order by salary desc) as rn3
from employee;

Windowed aggregate function

Windowed aggregate function ：SUM(), avg(), max(), min(), count()

The operation sample ：

select 
	dname, ename, salary,    
	sum(salary) over (partition by dname order by hiredate) as pv1,
	count(salary) over (partition by dname order by hiredate) as pv2
from employee;

--  Start with the third line and count down 
-- hiredate rows between 3 preceding and current row 
select 
	dname, ename, salary,    
	sum(salary) over (partition by dname order by hiredate rows between 3 preceding and current row ) as pv1
from employee;

Distribution function

Distribution function ：CUME_DIST() and PERCENT_RANK()

CUME_DIST()

purpose ： Less than... In the group 、 Equal to current rank The number of rows for the value / The total number of rows in the group

Example ：

select 
	dname, ename, salary,
	cume_dist() over( order by salary) as rn1,
	cume_dist() over(partition by dname order by salary) as rn2
from employee;

PERCENT_RANK()

purpose ： Each line follows the formula (rank-1) / row(rows-1) Calculate , among ,rank by RNAK() The sequence number generated by the function ,rows Record the total number of rows for the current window .

select 
	dname, ename, salary,
	rank() over( partition by dname order by salary) as rn1,
	percent_rank() over(partition by dname order by salary) as rn2
from employee;
/*  first line ： (1-1) / （6-1） = 0 row2: (1-1) / (6-1) = 0 row3: (3-1) / (6-1) = 0.4 */

Before and after function LAG and LEAD

Returns the line that precedes the current line n That's ok (lag(expr, n )) Or after n That's ok （LEAD(EXPR, N) ） Of expr value

--  Before and after function LAG and LEAD
select 
	dname, ename, salary, hiredate,
	lag(hiredate, 1, '2000-01-01') over( partition by dname order by hiredate ) as time1,
	lag(hiredate, 2) over(partition by dname order by hiredate) as time2
from employee;

Head tail function FIRST_VALUE() and lAST_VALUE

Introduce ：

purpose ： Return to the first （first_value(expr） Or the last one ( last_value(expr) ) expr Value

Application scenarios ： As of now , Query by date 1 The salary of the first and last employee

The operation sample ：

--  Head tail function  FIRST_VALUE()  and  lAST_VALUE
select 
	dname, ename, salary, hiredate,
	first_value(salary) over( partition by dname order by hiredate ) as first,
	last_value(salary) over(partition by dname order by hiredate) as last
from employee;

Other functions

NTH_VALUE(expr, n)

purpose ： Return to... In the window N individual Expr Value ,EXPR It could be an expression , It can also be listed

Application scenarios ： As of the current salary , Displays the salary ranking of each employee 2 Or 3 Pay for

The operation sample ：

select 
	dname, ename, salary, hiredate,
	nth_value(salary, 2) over( partition by dname order by salary ) as two,
	nth_value(salary, 3) over(partition by dname order by salary) as three
from employee;

--  Take out the first group of employees in each department 
select * from (
	select 
		dname, ename, hiredate, salary,
	ntile(3) over(partition by dname order by hiredate ) as rn
	from employee
) t
	where t.rn  = 1;