#一. Character function
#Calculate character length SELECT LENGTH('john')
#Display encoding format SHOW VARIABLES LIKE '%char%'
#Turn case
SELECT UPPER('john')
SELECT LOWER('JOHN')
SELECT SUBSTR('李莫愁爱上了陆展元',7) AS out_put
#Intercept stringSELECT SUBSTR('李莫愁爱上了陆展元',1,3) AS out_put
# Splicing stringSELECT CONCAT(UPPER(SUBSTR(last_name,1,1)),'_',LOWER(SUBSTR(last_name,2))) FROM employees
#Find index, return the actual indexSELECT INSTR('杨杨阿姨那个','阿姨')
#Remove spaces, remove spaces before and after
SELECT TRIM(' 666 ')
SELECT LENGTH(TRIM(' 666 '))
SELECT TRIM('a' FROM 'aaaaaa张aaaa无极aaaaaa')
#Fill the specified length with the specified characters
SELECT LPAD('赵子龙',10,'*')
SELECT RPAD('赵子龙',10,'*')
#Replace the specified stringSELECT REPLACE('***aaaa****','aaaa','bbbb')
#二. Mathematical Functions
# Rounding
SELECT ROUND(-1.56)
SELECT ROUND(1.46)
SELECT ROUND(1.462,2)
#Round up, return an integer greater than or equal to the parameter #Round SELECT CEIL(1.02)
down, return an integer less than or equal to the parameter
SELECT FLOOR(1.82)
#TruncationSELECT TRUNCATE(1.69999,2)
#取余SELECT MOD(10,3)
#三. Date function
SELECT NOW()
SELECT CURDATE()
SELECT CURTIME()
SELECT YEAR(NOW())
#Convert the specified characters into date format
SELECT STR_TO_DATE('2021-04-01','%Y-%m-%d')
SELECT STR_TO_DATE('2021-4-1','%Y-%c-%d')
#Convert the specified date into a stringSELECT DATE_FORMAT(NOW(),'%y年%m月%d日')
#四. Other functions
SELECT VERSION()
SELECT DATABASE()
SELECT USER()