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MySQL - common functions - string functions
2022-07-07 02:38:00 【Sauerkraut】
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;
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