A character function
Get the number of bytes 1.LENGTH-- parameter value
SELECT LENGTH('LALA');
Results: 4
2.CONCAT-- string concatenation
SELECT CONCAT('I','am','OK');
The results: IamOK
3.UPPER-- parameter capitalized
SELECT UPPER('abc');
The results: ABC
4.LOWER-- parameter lowercase
SELECT LOWER('ABC');
The results: abc
5.SUBSTR-- index starting from 1, and then returns the string specified position
SELECT SUBSTR('ABC',2);
The results: BC
SUBSTR-- taken starting at the specified index (second parameter), and after obtaining a string index position of the specified character length
SELECT SUBSTR('ABC',1,2);
The results: AB
6.INSTR-- returns the second parameter in the first parameter of the first occurrence of a position, if not occurred, it returns 0
SELECT INSTR('ABCD','CD');
Results: 3
7.TRIM-- removal of specified character from beginning to end, if not specified, then the removal of a space
SELECT SUBSTR('#','###ASD##123####');
Results: ASD ## 123
8.LPAD-- realization left to fill the specified length with the specified character, but also the result of the final length
SELECT LPAD('ABC',4,'#');
The results: #ABC
9.RPAD-- right padding to achieve a specified length with the specified characters, but also the results of the final length
SELECT LPAD('ABC',4,'#');
The results: ABC #
10.REPLACE-- replace all the specified string to another string
SELECT REPLACE('ABCABC','B','#');
The results: A # CA # C
Second, mathematical functions
1.ROUND-- rounding
SELECT ROUND(1.56);
Results: 2
ROUND-- preserve the specified number of decimal places
SELECT ROUND(3.1415926,2);
Results: 3.14
2.CEIL-- rounded up, returns greater than or equal to the smallest integer parameter
SELECT CEIL(-1.7836);
Result: -1
3.FLOOR-- rounded down, returns less than or equal to the greatest integer parameter
SELECT FLOOR(3.897);
Results: 3
4.TRUNCATE-- cut
SELECCT RUNCATE ( 1.668675 );
Results: 1.66
Modulo 5.MOD--
SELECT MOD(10,3);
Results: 1
Third, the date function
1.NOW-- returns the current date + time
SELECT NOW();
2.CURDATE-- Returns the current system date and time is not included
SELECT CURDATE();
3.CURTIME-- returns the current time, no date
SELECT CURTIME ();
4.MONTHNAME, DAYDATE etc. - return date English name
SELECT DAYDATE(NOW());
5.STR_TO_DATE-- string into a format specified by date
SELECT STR_TO_DATE('4-3#1998','%m-%d#%Y');
Results: 1998-04-03
6.DATE_FORMAT-- date into the specified format string
SELECT DATE_FORMAT(NOW(),'%m#%d#%Y');
Results: 09 # 04 # 2019
Third, other functions
The SELECT VERSION (); - obtaining sql version number
The SELECT DATABASE (); - get the current location database name
The SELECT the USER (); - for login user name
Fourth, the flow control function
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