MySQL - common functions - string functions

function

MySQL The function will process the parameters passed in , And return a processing result , That is, return a value .

MySQL Contains a large number and rich functions , Let's talk about dozens of commonly used , For the remaining rare functions, we can go to 「MySQL Reference manual 」 Inquire about .

String function

function	effect
UPPER( Column | character string )	Convert each character of the string to uppercase
LOWER( Column | character string )	Convert each character of the string to lowercase
CONCAT(str1,str2,. . . )	Connect all strings into one string
REPLACE( Column | character string , Old string , New string )	Replace the old string with the new string
LENGTH( Column | character string )	Find the string length
SUBSTR( Column | character string , Starting point [, length ])	String interception
LEFT(str,len)	Get the left side of the string len A string of characters
RIGHT(str,len)	Get the right side of the string len A string of characters
MID(str,pos,len)	Get the string from pos( Number one ) Position start , The length is len String
ASCII( character )	Returns the decimal integer corresponding to the specified character
CHR( Numbers )	Returns the character corresponding to an integer
RPAD( Column | character string , length , Fill character ) LPAD( Column | character string , length , Fill character )	Fill the right or left of the string with the specified character
LTRIM( character string )、RTRIM( character string )	Remove the left or right space of the string
TRIM( Column | character string )	Remove the space around the string
INSTR( Column | character string , String to find , Starting position , Location of occurrence )	Find out whether a substring appears at the specified position

UPPER( Column | character string )

Convert each character of the string to uppercase

If you use emp Table shows that the test data is output many times , because emp There are many pieces of data in the table , Every piece of data should be executed

Use MySQL Virtual tables in , There's only one line of data , It can be used to test functions , Or not

You can find ： If case is combined , Use LOWER All of them become lowercase

CONCAT(str1,str2,. . . )

Connect all strings into one string

Single and double quotation marks can be used for strings

If there are quotation marks in the string ' ' ', The escape character is required ' \ ' Transference

REPLACE( Column | character string , Old string , New string )

Replace the old string with the new string

LENGTH( Column | character string )

Find the string length

Get the left side of the string 2 A string of characters 、 Get the right side of the string 2 A string of characters 、 Get the middle of the string 2 A string of characters

LEFT(str,len)	Get the left side of the string len A string of characters
RIGHT(str,len)	Get the right side of the string len A string of characters
MID(str,pos,len)	Get the string from pos( Number one ) Position start , The length is len String

SELECT LEFT('hello',2),RIGHT('hello',2),MID('case',2,2);

ASCII( character )	Returns the decimal integer corresponding to the specified character
CHR( Numbers )	Returns the character corresponding to an integer

SELECT ASCII('A');

SELECT CHAR(65);

RPAD( Column | character string , length , Fill character ) LPAD( Column | character string , length , Fill character )

Fill the right or left of the string with the specified character

SELECT RPAD('Hello',10,'*'),LPAD('Hello',10,'*');

Fill the left and right sides 5 individual ' * ', Fill the right first , Treat the whole as a string , Fill in the front ' * '

SELECT LPAD(RPAD('Hello',10,'*'),15,'*');

LTRIM( character string )、RTRIM( character string )	Remove the left or right space of the string
TRIM( Column | character string )	Remove the space around the string

SELECT LTRIM('    123    *')  Left ,RTRIM('*    123    ')  Right ,TRIM('    123    ') AS 'All';

You can't remove the space in the middle of the string

INSTR( Column | character string , String to find , Starting position , Location of occurrence )

Find out whether a substring appears at the specified position

SELECT INSTR(' I love C Language ','C Language ');

Not found

1. Capitalize the employee's name Smith

SELECT UPPER(LEFT(ename,1)) FROM emp;

SELECT UPPER(LEFT(ename,1)),LOWER(SUBSTR(ename,2)) FROM emp;

SELECT CONCAT(UPPER(LEFT(ename,1)),LOWER(SUBSTR(ename,2))) FROM emp;

2. The length of the name is 5 All employee information for Or use fuzzy queries LIKE  MySQL --- Database query - Conditions of the query _ Xiaoxuecai's blog -CSDN Blog

SELECT * FROM emp WHERE LENGTH(ename)=5;

3. The first three letters of the employee's name are 'JAM' The employees' , Intercept start point and length

SELECT * FROM emp WHERE SUBSTR(ename,1,3)='JAM';

4. Query all employee information , But the first three letters of the name are not displayed

SUBSTR( Column | character string , Starting point [, length ])

String interception

SELECT ename  Original string ,SUBSTR(ename,3) AS ' Substring ' FROM emp;

Query all employee information , But only the last three letters of the name are displayed  

SUBSTR( Column | character string , Starting point [, length ])

String interception

SELECT ename  Original string ,SUBSTR(ename,-3) AS ' Substring ' FROM emp;