MySQL Basics - functions

Catalog

function

String function

Numerical function

Date function

Flow function

In the last article, we learned MySQL Basics ——DCL sentence , This article is for learning MySQL Basics —— function .

function

A function is a program or code that can be called directly by another program .

The following code demonstrates the data table structure and data as follows ：

String function

stay MySQL Common string functions are shown in the following table ：

function	function
CONCAT(S1,S2,...Sn)	String splicing , take S1,S2,...Sn Concatenate into a string
LOWER(str)	The string str All to lowercase
UPPER(str)	The string str Capitalize all
LPAD(str,n,pad)	padding-left , Use string pad Yes str Fill the left side of the , achieve n String length
RPAD(str,n,pad)	Right fill , Use string pad Yes str Fill the right side of the , achieve n String length
TRIM(str)	Remove the spaces at the beginning and end of the string
SUBSTRING(str,start,len)	Return from string str from start It's from the position len A string of length

The syntax format of using string function is as follows ：

 function ( Parameters );

The sample code is as follows ：

SELECT CONCAT('hello','world');         #  String concatenation 

As shown in the figure below ：

When we need to use string functions to operate on the data table , The sample code is as follows ：

UPDATE students SET uid =RPAD(uid,5,'0');       # Fill right uid
SELECT * FROM students;                     # View the data 

As shown in the figure below ：

Numerical function

stay MySQL The commonly used numerical functions are shown in the following table ：

function	function
CEIL(x)	Rounding up
FLOOR(x)	Rounding down
MOD(x,y)	return x/y The mold
RAND()	return 0~1 The random number in
ROUND(x,y)	Find parameters x Rounded value of , Retain y Decimal place

The syntax format for using numeric functions is as follows ：

 function ( Parameters );

The sample code is as follows ：

SELECT RAND();          # Random generation 0~1 The random number in 

As shown in the figure below ：

Date function

stay MySQL Common date functions are shown in the following table ：

function	function
CURDATE()	Return current date
CURTIME()	Return current time
NOW()	Returns the current date and time
YEAR(date)	Get specified date A year of
MONTH(date)	Get specified date Month of
DAY(date)	Get specified date Date
DATE_ADD(date,INTERVAL expr type)	Return a date / Time value plus a time interval expr Time value after
DATEDIFF(date1,date2)	Return to start time date1 And end time date2 Days between

The syntax format of the date function is as follows ：

 function ( Parameters );

The sample code is as follows ：

SELECT CURDATE();                   #  Get the current time 
SELECT YEAR(CURDATE());             #  Get the year of the current time 
SELECT DATE_ADD(CURDATE(),INTERVAL 70 DAY);     # Gets the current time plus 70 God 

As shown in the figure below ：

Flow function

stay MySQL Common process functions are shown in the following table ：

function	function
IF(value,t,f)	If value by true, Then return to t, Otherwise return to f
IFNULL(value1,value2)	If value1 Not empty , return value1, Otherwise return to value2
CASE WHEN [val1] THEN [res1] ... ELSE [default] END	If val1 by true, return res1,... Otherwise return to default The default value is
CASE [expr] WHEN [val1] THEN [res1] ... ELSE [default] END	If expr The value is equal to the val1, return res1,... Otherwise return to default The default value is

The syntax format of the process function is as follows ：

 function ( Parameters );

The sample code is as follows ：

SELECT IF(true,'OK','Error');		
SELECT IFNULL(NULL,'OK');
SELECT uname ,(CASE usex WHEN ' male ' THEN '1' WHEN ' Woman ' THEN '2' ELSE '0' END) AS ' Gender ' FROM students;

As shown in the figure below ：

Okay ,MySQL Basics —— That's all for the function , In the next article, we will learn MySQL Basics —— constraint ​​​​​​​.