Summary of MySQL commonly used functions

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1. Numeric functions
• 2. String functions
• 3 , Date function
• 4. MySQL advanced functions

(1) Numeric function

1. ABS(x) Return The absolute value of x

SELECT ABS(-1); ---- 返回1

2. AVG(expression) returns the average of an expression, expression is a field

SELECT AVG(age) FROM student;

3. CEIL(x)/CEILING(x) returns the smallest integer greater than or equal to x

SELECT CEIL(1.5); SELECT CEILING(1.5); ---- 返回2

4.FLOOR(x ) Returns the largest integer less than or equal to x

SELECT FLOOR(1.5); ---- 返回1

5, EXP(x) Returns e raised to the power of x

SELECT EXP(3); ---- 计算 e 的三次方,返回20.085536923188

6, GREATEST (expr1, expr2, expr3, …) Returns the maximum value in the list

SELECT GREATEST(3, 12, 34, 8, 25); ---- 返回以下数字列表中的最大值34

7, LEAST(expr1, expr2, expr3, …) Returns the minimum value in the list

SELECT LEAST(3, 12, 34, 8, 25); ---- 返回以下数字列表中的最小值3

8. LN returns the natural logarithm of the number

SELECT LN(2); ---- 返回 2 的自然对数：0.6931471805599453

9. LOG(x) returns the natural logarithm (logarithm with base e)

SELECT LOG(20.085536923188); ---- 返回 3

10. MAX(expression) returns the maximum value in field expression

SELECT MAX(age) AS maxAge FROM Student; ---- age最大值

11.MIN(expression) returns the maximum value in field expression Maximum value

SELECT MIN(age) AS minAge FROM Student; ---- age最小值

12. POW(x,y)/POWER(x,y) returns x raised to the power of y

SELECT POW(2,3); SELECT POWER(2,3); ---- 返回2 的 3 次方：8

13 , RAND() returns a random number from 0 to 1

SELECT RAND(); ---- 返回 0 到 1 的随机数，若()里面有数字,RAND(x),x相同时，返回值相同

14, ROUND(x) returns the nearest integer to x

SELECT ROUND(1.23456); ---- 返回 1

15 , SIGN(x) returns the sign of x, x is a negative number, 0, and positive number returns -1, 0 and 1 respectively

SELECT SIGN(-10); ---- 返回 -1

16. SQRT(x) returns the square root of x

SELECT SQRT(25); ---- 返回5

17. SUM(expression) returns the sum of the specified field

SELECT SUM(age) AS totalAage FROM Student; ---- 返回age的总和

18. TRUNCATE(x,y) returns the value x to the decimal point The value of the last y digit (the biggest difference from ROUND is that it will not be rounded)

SELECT TRUNCATE(1.23456,3); ---- 返回1.234

(2) String function

1, Returns the ASCII code of the first character of string s

SELECT ASCII('AB'); ---- 返回A的ASCII码值：65

2. LENGTH/CHAR_LENGTH(s)/CHARACTER_LENGTH(s) returns the number of characters of string s

SELECT LENGTH('1234'); ---- 返回4

3. CONCAT(s1,s2…sn) strings s1, s2 and other strings are combined into one string

SELECT CONCAT('hel','llo'); ---- 返回hello

4.FIND_IN_SET( s1, s2) returns the position of the string matching s1 in string s2

SELECT FIND_IN_SET("c", "a,b,c,d,e"); ---- 返回3

5. The FORMAT(x,n) function can format the number x "#,.##", keep x to n digits after the decimal point, and round the last digit

SELECT FORMAT(250500.5634, 2); ---- 返回250,500.56

6, INSERT(s1,x,len,s2) string s2 replacement The x position of s1 starts a string of length len

SELECT INSERT("google.com", 1, 6, "runnob"); ---- 返回runoob.com

7. LOCATE(s1,s) gets the starting position of s1 from the string s

SELECT LOCATE('st','myteststring'); ---- 返回5

8, LCASE(s)/LOWER(s) turns all letters of string s into lowercase letters

SELECT LOWER('RUNOOB'); ---- 返回runoob

9, UCASE(s)/UPPER(s )Convert all letters of string s into uppercase letters

SELECT UCASE('runoob'); ---- 返回RUNOOB

10. TRIM(s) remove the spaces at the beginning and end of string s

SELECT TRIM(' RUNOOB '); ---- 返回RUNOOB

11. LTRIM(s) removes the spaces at the beginning of the string s

SELECT LTRIM(' RUNOOB '); ---- 返回 ’RUNOOB ‘

12. RTRIM(s) removes the spaces at the end of the string s

SELECT RTRIM(' RUNOOB '); ---- 返回 ’ RUNOOB‘

13. SUBSTR(s, start, length) intercepts a substring of length length from the start position of string s

SELECT SUBSTR("RUNOOB", 2, 3) AS ExtractString; ---- 从字符串 RUNOOB 中的第 2 个位置截取 3个 字符，返回UNO

14.SUBSTR/ SUBSTRING(s, start, length) intercepts a substring of length from the start position of string s

SELECT SUBSTR/SUBSTRING("RUNOOB", 2, 3); ---- 从字符串 RUNOOB 中的第 2 个位置截取 3个 字符，返回UNO

15. POSITION(s1 IN s) obtains from string s The starting position of s1

SELECT POSITION('b' in 'abc'); ---- 返回2

16. REPEAT(s,n) repeats the string s n times

SELECT REPEAT('runoob',3); ---- 返回runoobrunoobrunoob

17.REVERSE(s )Reverse the order of string s

SELECT REVERSE('abc'); ---- 返回cba

18. STRCMP(s1,s2) compares strings s1 and s2. If s1 and s2 are equal, return 0. If s1>s2, return 1. If s1

SELECT STRCMP("runoob", "runoob"); ---- 返回0

(3) Date function

1, CURDATE()/CURRENT_DATE() returns the current Date

SELECT CURDATE(); SELECT CURRENT_DATE(); ---- 返回2019-02-19

2. CURRENT_TIME()/CURTIME() returns the current time

SELECT CURRENT_TIME(); ---- 返回11:40:45

3. CURRENT_TIMESTAMP() returns the current date and time

SELECT CURRENT_TIMESTAMP(); ---- 返回2019-02-19 11:41:32

4. ADDDATE(d,n) calculates the start date d plus n days’ date

SELECT ADDDATE("2017-06-15", INTERVAL 10 DAY); ---- 返回2017-06-25

5. ADDTIME(t, n) Time t plus n seconds of time

SELECT ADDTIME('2011-11-11 11:11:11', 5); ---- 返回2011-11-11 11:11:16

6. DATE() extracts the date value from the date or datetime expression

SELECT DATE("2017-06-15 11:11:16"); ---- 返回2017-06-15

7. DAY(d) returns the date part of date value d

SELECT DAY("2017-06-15"); ---- 返回15

8、DATEDIFF(d1,d2)计算日期 d1->d2 之间相隔的天数

SELECT DATEDIFF('2001-01-01','2001-02-02'); ---- 返回-32

9、DATE_FORMAT按表达式 f的要求显示日期 d

SELECT DATE_FORMAT('2011.11.11 11:11:11','%Y-%m-%d %r'); ---- 返回2011-11-11 11:11:11 AM

10、DAYNAME(d)返回日期 d 是星期几，如 Monday,Tuesday

SELECT DAYNAME('2011-11-11 11:11:11'); ---- 返回Friday

11、DAYOFMONTH(d)计算日期 d 是本月的第几天

SELECT DAYOFMONTH('2011-11-11 11:11:11'); ---- 返回11

12、DAYOFWEEK(d)日期 d 今天是星期几，1 星期日，2 星期一，以此类推

SELECT DAYOFWEEK('2011-11-11 11:11:11'); ---- 返回6

13、DAYOFYEAR(d)计算日期 d 是本年的第几天

SELECT DAYOFYEAR('2011-11-11 11:11:11'); ---- 返回315

14、EXTRACT(type FROM d)从日期 d 中获取指定的值，type 指定返回的值
type可取值为：
MICROSECOND
SECOND
MINUTE
HOUR
DAY
WEEK
MONTH
QUARTER
YEAR
SECOND_MICROSECOND
MINUTE_MICROSECOND
MINUTE_SECOND
HOUR_MICROSECOND
HOUR_SECOND
HOUR_MINUTE
DAY_MICROSECOND
DAY_SECOND
DAY_MINUTE
DAY_HOUR
YEAR_MONTH

SELECT EXTRACT(MINUTE FROM '2011-12-13 14:15:16'); ---- 返回15

15、DAYOFWEEK(d)日期 d 今天是星期几，1 星期日，2 星期一，以此类推

SELECT DAYOFWEEK('2011-11-11 11:11:11'); ---- 返回6

16、UNIX_TIMESTAMP()得到时间戳

SELECT UNIX_TIMESTAMP('2019-2-19'); SELECT UNIX_TIMESTAMP(expression); ---- 返回1550505600

17、FROM_UNIXTIME()时间戳转日期

SELECT FROM_UNIXTIME(1550505600); ---- 返回2019-02-19 00:00:00 SELECT FROM_UNIXTIME(1550505600, '%Y-%m-%d'); ---- 返回2019-02-19

（四）MySQL高级函数

1、IF(expr,v1,v2)如果表达式 expr 成立，返回结果 v1；否则，返回结果 v2

SELECT IF(1>0,'yes','no'); ---- 返回yes

2、CONV(x,f1,f2)返回 f1 进制数变成 f2 进制数

SELECT CONV(13,10,2); ---- 返回1101

3、CURRENT_USER()/SESSION_USER()/SYSTEM_USER()/USER()返回当前用户
4、DATABASE()返回当前数据库名
5、VERSION()返回数据库的版本号

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