MySQL function

function

• String function
• Numerical function
• Date function
• Flow function

String function

Common functions ：

function	function
CONCAT(s1, s2, …, sn)	String splicing , take s1, s2, …, sn Concatenate into a string
LOWER(str)	Convert all strings to lowercase
UPPER(str)	Convert all strings to uppercase
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

Examples of use ：

--  Splicing SELECT CONCAT('Hello', 'World');--  A lowercase letter SELECT LOWER('Hello');--  Capitalization SELECT UPPER('Hello');--  padding-left SELECT LPAD('01', 5, '-');--  Right fill SELECT RPAD('01', 5, '-');--  Remove the space SELECT TRIM(' Hello World ');--  section （ The starting index is 1）SELECT SUBSTRING('Hello World', 1, 5);

Numerical function

Common function ：

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 Round the value of , Retain y Decimal place

Date function

Common functions ：

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

Example ：

-- DATE_ADDSELECT DATE_ADD(NOW(), INTERVAL 70 YEAR);

Flow function

Common functions ：

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

Example ：

select    name,    (case when age > 30 then ' middle-aged ' else ' youth ' end)from employee;select    name,    (case workaddress when ' The Beijing municipal ' then ' first-tier cities ' when ' Shanghai ' then ' first-tier cities ' else ' Second-tier cities ' end) as ' Work address 'from employee;