What are the mysql string functions?

mysql string functions include: 1. LOWER, convert the string parameter value to all lowercase letters and return; 2. UPPER, convert the string parameter value to all uppercase letters and return; 3. CONCAT, Return multiple string parameters concatenated end to end; 4. SUBSTR, starting from the specified position pos in the source string str.

mysql string functions are:

1, LOWER(column|str): Convert the string parameter value to all lowercase letters and return

mysql> select lower('SQL Course');+---------------------+
| lower('SQL Course') |
+---------------------+
| sql course          |
+---------------------+

2, UPPER(column| str): Convert the string parameter value to all uppercase letters and return

mysql> select upper('Use MYsql');+--------------------+
| upper('Use MYsql') |
+--------------------+
| USE MYSQL          |
+--------------------+

3, CONCAT(column|str1, column| str2,...): Return after concatenating multiple string parameters end to end

mysql> select concat('My','S','QL');+-----------------------+
| concat('My','S','QL') |
+-----------------------+
| MySQL                 |
+-----------------------+

If any parameter is null, the function returns null

mysql> select concat('My',null,'QL');+------------------------+
| concat('My',null,'QL') |
+------------------------+
| NULL                   |
+------------------------+

If the parameter is a number, Then it will be automatically converted into a string

mysql> select concat(14.3,'mysql');+----------------------+
| concat(14.3,'mysql') |
+----------------------+
| 14.3mysql            |
+----------------------+

4. CONCAT_WS(separator,str1,str2,...):Convert multiple string parameters to the given The separator separator is connected end to end and returns

mysql> select concat_ws(';','First name','Second name','Last name');+-------------------------------------------------------+
| concat_ws(';','First name','Second name','Last name') |
+-------------------------------------------------------+
| First name;Second name;Last name                      |
+-------------------------------------------------------+

! ! That is, the first item in the function parentheses is used to specify the separator

5, SUBSTR(str,pos[,len]): From the specified position in the source string str pos starts taking a string and returns

Note:

①len specifies the length of the substring. If omitted, it will be taken to the end of the string; a negative value of len means starting from the source string The tail begins to pick up.

　②Function SUBSTR() is a synonym of function SUBSTRING().

mysql> select substring('hello world',5);+----------------------------+
| substring('hello world',5) |
+----------------------------+
| o world                    |
+----------------------------+mysql> select substr('hello world',5,3);+---------------------------+
| substr('hello world',5,3) |
+---------------------------+
| o w                       |
+---------------------------+mysql> select substr('hello world',-5);+--------------------------+
| substr('hello world',-5) |
+--------------------------+
| world                    |
+--------------------------+

6. LENGTH(str): Returns the storage length of the string

mysql> select length('text'),length('你好');+----------------+------------------+
| length('text') | length('你好')   |
+----------------+------------------+
|              4 |                6 |
+----------------+------------------+

Note: The storage length of the string depends on the encoding method. Different ('Hello': utf8 is 6, gbk is 4)

7, CHAR_LENGTH(str): Return string The number of characters in

mysql> select char_length('text'),char_length('你好');+---------------------+-----------------------+
| char_length('text') | char_length('你好')   |
+---------------------+-----------------------+
|                   4 |                     2 |
+---------------------+-----------------------+

8. INSTR(str, substr): Return the substring substr from the source string str The position of an occurrence

mysql> select instr('foobarbar','bar');+--------------------------+
| instr('foobarbar','bar') |
+--------------------------+
|                        4 |
+--------------------------+

9. LPAD(str, len, padstr): Padding the given left side of the source string character padstr to the specified length len, and return the filled string

mysql> select lpad('hi',5,'??');+-------------------+
| lpad('hi',5,'??') |
+-------------------+
| ???hi             |
+-------------------+

10. RPAD(str, len, padstr): Padding the given character padstr to the specified length len on the right side of the source string, and returning the filled string

mysql> select rpad('hi',6,'??');+-------------------+| rpad('hi',6,'??') |+-------------------+| hi????            |+-------------------+

11. TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str), TRIM([remstr FROM] str):

Remove both ends, prefixes or The suffix character remstr is returned;

If remstr is not specified, the spaces at both ends of str will be removed; if BOTH, LEADING, and TRAILING are not specified, the default is BOTH.

mysql> select trim('  bar  ');+-----------------+
| trim('  bar  ') |
+-----------------+
| bar             |
+-----------------+mysql> select trim(leading 'x' from 'xxxbarxxx');+------------------------------------+
| trim(leading 'x' from 'xxxbarxxx') |
+------------------------------------+
| barxxx                             |
+------------------------------------+mysql> select trim(both 'x' from 'xxxbarxxx');+---------------------------------+
| trim(both 'x' from 'xxxbarxxx') |
+---------------------------------+
| bar                             |
+---------------------------------+mysql> select trim(trailing 'xyz' from 'barxxyz');+-------------------------------------+
| trim(trailing 'xyz' from 'barxxyz') |
+-------------------------------------+
| barx                                |
+-------------------------------------+

12. REPLACE(str, from_str, to_str): Find all substrings form_str (case sensitive) in the source string str, and find them Replace it with the replacement string to_str. Return the replaced string

mysql> select replace('www.mysql.com','w','Ww');+-----------------------------------+
| replace('www.mysql.com','w','Ww') |
+-----------------------------------+
| WwWwWw.mysql.com                  |
+-----------------------------------+

13, LTRIM (str), RTRIM (str): Remove the left or right side of the string Spaces (left justified, right justified)

mysql> SELECT  ltrim('   barbar   ') rs1, rtrim('   barbar   ') rs2;+-----------+-----------+
| rs1       | rs2       |
+-----------+-----------+
| barbar    |    barbar |
+-----------+-----------+

14. REPEAT(str, count): Repeat the string str count times Then return

mysql> select repeat('MySQL',3);+-------------------+
| repeat('MySQL',3) |
+-------------------+
| MySQLMySQLMySQL   |
+-------------------+

15. REVERSE(str): Reverse the string str and return

mysql> select reverse('abcdef');+-------------------+
| reverse('abcdef') |
+-------------------+
| fedcba            |
+-------------------+

##16, CHAR(N,... [USING charset_name]): Interpret each parameter N as an integer (character encoding), and return each A string consisting of characters corresponding to an integer (NULL values ​​are ignored).

mysql> select char(77,121,83,81,'76'),char(77,77.3,'77.3');+-------------------------+----------------------+
| char(77,121,83,81,'76') | char(77,77.3,'77.3') |
+-------------------------+----------------------+
| MySQL                   | MMM                  |
+-------------------------+----------------------+

By default, the function returns a binary string. If you want to return a string for a specific character set, use the using option

mysql> SELECT charset(char(0x65)), charset(char(0x65 USING utf8));+---------------------+--------------------------------+
| charset(char(0x65)) | charset(char(0x65 USING utf8)) |
+---------------------+--------------------------------+
| binary              | utf8                           |
+---------------------+--------------------------------+

17. FORMAT(X,D[,locale]): Format the number X

• in the format '#,

  ,

  .##' D specifies the number of decimal places

• locale specifies the national language (the default locale is en_US)

mysql> SELECT format(12332.123456, 4), format(12332.2,0); ---------------------------------- ------------------ -
| format(12332.123456, 4) | format(12332.2,0) |
----------------------- --- ----------------
| 12,332.1235 | 12,332 |
----------------------- ------------------- mysql> SELECT format(12332.2,2,'de_DE'); --------------- ------------
| format(12332.2,2,'de_DE') |
-------------------- -------
| 12.332,20                 |
---------------------------

18. SPACE(N):

Returns a string consisting of N spaces

mysql> select space(3);+----------+
| space(3) |
+----------+
|          |
+----------+

###

19、LEFT(str, len)：返回最左边的len长度的子串

mysql> select left('chinaitsoft',5);+-----------------------+
| left('chinaitsoft',5) |
+-----------------------+
| china                 |
+-----------------------+

20、RIGHT(str, len)：返回最右边的len长度的子串

mysql> select right('chinaitsoft',5);+------------------------+
| right('chinaitsoft',5) |
+------------------------+
| tsoft                  |
+------------------------+

21、STRCMP(expr1,expr2)：如果两个字符串是一样的则返回0；如果第一个小于第二个则返回-1；否则返回1

mysql> select strcmp('text','text');+-----------------------+
| strcmp('text','text') |
+-----------------------+
|                     0 |
+-----------------------+mysql> SELECT strcmp('text', 'text2'),strcmp('text2', 'text');+-------------------------+-------------------------+
| strcmp('text', 'text2') | strcmp('text2', 'text') |
+-------------------------+-------------------------+
|                      -1 |                       1 |
+-------------------------+-------------------------+

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