Tutorial on principles and applications of database system (053) -- MySQL query (XV): usage of character functions

Database system principle and Application Tutorial （053）—— MySQL Inquire about （ 15、 ... and ）： Usage of character function

Using functions when querying can construct more flexible query conditions ,MySQL Provides functions for processing strings .

One 、 Create data table

The data table used for query is as follows ：

--  Table structure 
mysql> desc student;
+--------+--------------+------+-----+---------+-------+
| Field  | Type         | Null | Key | Default | Extra |
+--------+--------------+------+-----+---------+-------+
| s_id   | char(5)      | NO   | PRI | NULL    |       |
| s_name | char(20)     | YES  |     | NULL    |       |
| gender | char(1)      | YES  |     | NULL    |       |
| birth  | datetime     | YES  |     | NULL    |       |
| phone  | char(20)     | YES  |     | NULL    |       |
| addr   | varchar(100) | YES  |     | NULL    |       |
+--------+--------------+------+-----+---------+-------+
6 rows in set (0.10 sec)

--  Table data 
mysql> select * from student;
+-------+-----------+--------+---------------------+-------------+-----------+
| s_id  | s_name    | gender | birth               | phone       | addr      |
+-------+-----------+--------+---------------------+-------------+-----------+
| S2011 |  Zhang Xiaogang     |  male      | 1999-12-03 00:00:00 | 13163735775 |  Xinyang City     |
| S2012 |  Liu Xiaoqing     |  Woman      | 1999-10-11 00:00:00 | 13603732255 |  Xinxiang City     |
| S2013 |  Cao mengde     |  male      | 1998-02-13 00:00:00 | 13853735522 |  Zhengzhou city     |
| S2014 |  Liu Yan       |  Woman      | 1998-06-24 00:00:00 | 13623735335 |  Zhengzhou city     |
| S2015 |  Liu Yan       |  Woman      | 1999-07-06 00:00:00 | 13813735225 |  Xinyang City     |
| S2016 |  Liu Ruofei     |  Woman      | 2000-08-31 00:00:00 | 13683735533 |  Kaifeng City     |
| S2021 |  Dong Wenhua     |  Woman      | 2000-07-30 00:00:00 | 13533735564 |  Kaifeng City     |
| S2022 |  Zhou Huajian     |  male      | 1999-05-25 00:00:00 | 13243735578 |  Zhengzhou city     |
| S2023 |  trump     |  male      | 1999-06-21 00:00:00 | 13343735588 |  Xinxiang City     |
| S2024 |  Obama     |  male      | 2000-10-17 00:00:00 | 13843735885 |  Xinyang City     |
| S2025 |  Zhou Jianhua     |  male      | 2000-08-22 00:00:00 | 13788736655 |  Kaifeng City     |
| S2026 |  Zhang Xueyou     |  male      | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |
| S2031 |  Lee Myung Bak     |  Woman      | 1999-10-26 00:00:00 | 13643732222 |  Zhengzhou city     |
| S2032 |  Vinci     |  male      | 1999-12-31 00:00:00 | 13043731234 |  Zhengzhou city     |
+-------+-----------+--------+---------------------+-------------+-----------+
14 rows in set (0.00 sec)

Two 、 Character processing functions

1、ASCII() function

Returns the... Of a character ASCII code , If the parameter is a string , Returns the first character ASCII code .

The syntax is as follows ：

--  The parameters of the function are characters 
--  If the parameter is a string , Returns the... Of the first character in the string  ASCII  code 
ASCII(str)

2、CHAR() function

The multiple ASCII Code is converted to the corresponding character , And connect it into a string .

The syntax is as follows ：

--  Parameters are several representations  ASCII  Integer of code 
--  Return from  n1,n2,…  Of  ASCII  Code corresponding to the character string 
CHAR(n1, n2, ...)

for example ：

mysql> select ascii('a') lower,char(ascii('a')-32) upper;
+-------+-------+
| lower | upper |
+-------+-------+
|    97 | A     |
+-------+-------+
1 row in set (0.00 sec)

mysql> select ascii('b') lower,char(ascii('b')-32) upper;
+-------+-------+
| lower | upper |
+-------+-------+
|    98 | B     |
+-------+-------+
1 row in set (0.00 sec)

3、 ... and 、 Evaluate string length function

1、CHAR_LENGTH() function

Returns the number of characters contained in the string （ Both Chinese and Western characters are counted as one character ）.

The syntax is as follows ：

--  The parameter of the function is a string 
--  Returns the number of characters contained in the string , Including half width characters and full width characters 
CHAR_LENGTH(str)

for example ：

/* select s_id, char_length(s_id), s_name, char_length(s_name) from student where addr=' Zhengzhou city '; */
mysql> select s_id, char_length(s_id), s_name, char_length(s_name) 
    -> from student where addr=' Zhengzhou city ';
+-------+-------------------+-----------+---------------------+
| s_id  | char_length(s_id) | s_name    | char_length(s_name) |
+-------+-------------------+-----------+---------------------+
| S2013 |                 5 |  Cao mengde     |                   3 |
| S2014 |                 5 |  Liu Yan       |                   2 |
| S2022 |                 5 |  Zhou Huajian     |                   3 |
| S2026 |                 5 |  Zhang Xueyou     |                   3 |
| S2031 |                 5 |  Lee Myung Bak     |                   3 |
| S2032 |                 5 |  Vinci     |                   3 |
+-------+-------------------+-----------+---------------------+
6 rows in set (0.12 sec)

2、LENGTH() function

Returns the length of a string , In bytes .

The syntax is as follows ：

--  The parameter of the function is a string 
--  Returns the length of the string （ The unit is byte ）
--  The length of multibyte characters depends on the character set used . such as  utf8mb4  A Chinese character in the character set is  4  Bytes ,utf8  A Chinese character in the character set is  3  Bytes , and  latin1  A Chinese character in the character set is  2  byte .
LENGTH(str)

for example ：

/* select s_id, length(s_id), s_name, length(s_name) from student where addr=' Zhengzhou city '; */
mysql> select s_id, length(s_id), s_name, length(s_name) 
    -> from student where addr=' Zhengzhou city ';
+-------+--------------+-----------+----------------+
| s_id  | length(s_id) | s_name    | length(s_name) |
+-------+--------------+-----------+----------------+
| S2013 |            5 |  Cao mengde     |              9 |
| S2014 |            5 |  Liu Yan       |              6 |
| S2022 |            5 |  Zhou Huajian     |              9 |
| S2026 |            5 |  Zhang Xueyou     |              9 |
| S2031 |            5 |  Lee Myung Bak     |              9 |
| S2032 |            5 |  Vinci     |              9 |
+-------+--------------+-----------+----------------+
6 rows in set (0.02 sec)

-- student  The character set used in the table is  utf8, A Chinese character is  3  Bytes 
mysql> show create table student\G
*************************** 1. row ***************************
       Table: student
Create Table: CREATE TABLE `student` (
  `s_id` char(5) NOT NULL,
  `s_name` char(20) DEFAULT NULL,
  `gender` char(1) DEFAULT NULL,
  `birth` datetime DEFAULT NULL,
  `phone` char(20) DEFAULT NULL,
  `addr` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`s_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.04 sec)

Four 、 Connection string function

1、CONCAT() function

Connect two or more strings into one string .

The syntax is as follows ：

--  The parameters of the function are several strings 
--  Connect the strings contained in the parameters into a string , Then return 
CONCAT(str1,str2,...)

for example ：

/* select concat(s_name, ':', phone, ':', addr) name_phone_addr from student where addr=' Zhengzhou city '; */
mysql> select concat(s_name, ':', phone, ':', addr) name_phone_addr 
    -> from student where addr=' Zhengzhou city ';
+---------------------------------+
| name_phone_addr                 |
+---------------------------------+
|  Cao mengde :13853735522: Zhengzhou city        |
|  Liu Yan :13623735335: Zhengzhou city          |
|  Zhou Huajian :13243735578: Zhengzhou city        |
|  Zhang Xueyou :13743735566: Zhengzhou city        |
|  Lee Myung Bak :13643732222: Zhengzhou city        |
|  Vinci :13043731234: Zhengzhou city        |
+---------------------------------+
6 rows in set (0.00 sec)

2、CONCAT_WS() function

Used for the connection of multiple strings , and CONCAT() Function , This function can specify the separator between multiple strings .

The syntax is as follows ：

--  The first parameter is the separator between strings when connecting strings 
--  Connect the strings contained in the parameters into a string , And separated by the specified separator 
CONCAT_WS(separator,st1,st2,...)

for example ：

/* select concat_ws(':', s_name, phone, addr) name_phone_addr from student where addr=' Zhengzhou city '; */
mysql> select concat_ws(':', s_name, phone, addr) name_phone_addr 
    -> from student where addr=' Zhengzhou city ';
+---------------------------------+
| name_phone_addr                 |
+---------------------------------+
|  Cao mengde :13853735522: Zhengzhou city        |
|  Liu Yan :13623735335: Zhengzhou city          |
|  Zhou Huajian :13243735578: Zhengzhou city        |
|  Zhang Xueyou :13743735566: Zhengzhou city        |
|  Lee Myung Bak :13643732222: Zhengzhou city        |
|  Vinci :13043731234: Zhengzhou city        |
+---------------------------------+
6 rows in set (0.00 sec)

3、GROUP_CONCAT() function

Connect all the data contained in a column , You can specify the separator between each data （ Default to comma ）, It is often used in grouping queries .

The syntax is as follows ：

--  This function processes a column in the table , Connect all the data contained in this column 
--  This function is generally used for grouping queries , Its usage is similar to aggregate function 
--  Connect all the data contained in a column , from  separator  Parameter specifies the separator , If omitted  separator, The default separator is comma 
-- distinct  Parameters are used to remove duplicate data 
-- order by  Parameter specifies to sort by a field in the table before connecting 
GROUP_CONCAT([distinct] fieldname [order by  Sort field  asc|desc] separator ' Separator ')

for example ：

（1） Do not specify separator , Default to comma

mysql> select addr, group_concat(s_name) name from student group by addr;
+-----------+----------------------------------------------------------+
| addr      | name                                                     |
+-----------+----------------------------------------------------------+
|  Xinyang City     |  Zhang Xiaogang , Liu Yan , Obama                                        |
|  Kaifeng City     |  Liu Ruofei , Dong Wenhua , Zhou Jianhua                                      |
|  Xinxiang City     |  Liu Xiaoqing , trump                                             |
|  Zhengzhou city     |  Cao mengde , Liu Yan , Zhou Huajian , Zhang Xueyou , Lee Myung Bak , Vinci                   |
+-----------+----------------------------------------------------------+
4 rows in set (0.08 sec)

（2） Specify the separator

mysql> select addr, group_concat(s_name separator '||') name from student group by addr;
+-----------+---------------------------------------------------------------+
| addr      | name                                                          |
+-----------+---------------------------------------------------------------+
|  Xinyang City     |  Zhang Xiaogang || Liu Yan || Obama                                           |
|  Kaifeng City     |  Liu Ruofei || Dong Wenhua || Zhou Jianhua                                         |
|  Xinxiang City     |  Liu Xiaoqing || trump                                                 |
|  Zhengzhou city     |  Cao mengde || Liu Yan || Zhou Huajian || Zhang Xueyou || Lee Myung Bak || Vinci                   |
+-----------+---------------------------------------------------------------+
4 rows in set (0.00 sec)

（3） Remove duplicate data when connecting

mysql> select group_concat(addr) addr from student;
+------------------------------------------------------------------------------------+
| addr 
+------------------------------------------------------------------------------------+
|  Xinyang City , Xinxiang City , Zhengzhou city , Zhengzhou city , Xinyang City , Kaifeng City , Kaifeng City , Zhengzhou city , Xinxiang City , Xinyang City , Kaifeng City , Zhengzhou city , Zhengzhou city , Zhengzhou city 
+------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select group_concat(distinct addr) addr from student;
+-----------------------------------------+
| addr                                    |
+-----------------------------------------+
|  Xinyang City , Kaifeng City , Xinxiang City , Zhengzhou city              |
+-----------------------------------------+
1 row in set (0.02 sec)

（4） Sort by a column before connecting

mysql> select s_id, s_name, addr from student where addr=' Zhengzhou city ' order by s_id desc;
+-------+-----------+-----------+
| s_id  | s_name    | addr      |
+-------+-----------+-----------+
| S2032 |  Vinci     |  Zhengzhou city     |
| S2031 |  Lee Myung Bak     |  Zhengzhou city     |
| S2026 |  Zhang Xueyou     |  Zhengzhou city     |
| S2022 |  Zhou Huajian     |  Zhengzhou city     |
| S2014 |  Liu Yan       |  Zhengzhou city     |
| S2013 |  Cao mengde     |  Zhengzhou city     |
+-------+-----------+-----------+
6 rows in set (0.01 sec)

mysql> select addr, group_concat(s_name) name from student where addr=' Zhengzhou city ';
+-----------+----------------------------------------------------------+
| addr      | name                                                     |
+-----------+----------------------------------------------------------+
|  Zhengzhou city     |  Cao mengde , Liu Yan , Zhou Huajian , Zhang Xueyou , Lee Myung Bak , Vinci                   |
+-----------+----------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select addr, group_concat(s_name order by s_id desc) name from student where addr=' Zhengzhou city ';
+-----------+----------------------------------------------------------+
| addr      | name                                                     |
+-----------+----------------------------------------------------------+
|  Zhengzhou city     |  Vinci , Lee Myung Bak , Zhang Xueyou , Zhou Huajian , Liu Yan , Cao mengde                   |
+-----------+----------------------------------------------------------+
1 row in set (0.00 sec)

5、 ... and 、 String replacement function

1、INSERT() function

Replace some characters in a string with other characters .

The syntax is as follows ：

--  Put the string  str  from  pos  The position begins  len  Replace characters with  instr  character string , And return the replaced string 
--  If  pos  Exceeds string length , Then no replacement will be made , Return the original string directly .
INSERT(str,pos,len,instr)

for example ： hold phone Medium 4-7 Replace characters with 【*】

mysql> select s_id,s_name,phone,insert(phone,4,4,'****') phone11 from student;
+-------+-----------+-------------+-------------+
| s_id  | s_name    | phone       | phone11     |
+-------+-----------+-------------+-------------+
| S2011 |  Zhang Xiaogang     | 13163735775 | 131****5775 |
| S2012 |  Liu Xiaoqing     | 13603732255 | 136****2255 |
| S2013 |  Cao mengde     | 13853735522 | 138****5522 |
| S2014 |  Liu Yan       | 13623735335 | 136****5335 |
| S2015 |  Liu Yan       | 13813735225 | 138****5225 |
| S2016 |  Liu Ruofei     | 13683735533 | 136****5533 |
| S2021 |  Dong Wenhua     | 13533735564 | 135****5564 |
| S2022 |  Zhou Huajian     | 13243735578 | 132****5578 |
| S2023 |  trump     | 13343735588 | 133****5588 |
| S2024 |  Obama     | 13843735885 | 138****5885 |
| S2025 |  Zhou Jianhua     | 13788736655 | 137****6655 |
| S2026 |  Zhang Xueyou     | 13743735566 | 137****5566 |
| S2031 |  Lee Myung Bak     | 13643732222 | 136****2222 |
| S2032 |  Vinci     | 13043731234 | 130****1234 |
+-------+-----------+-------------+-------------+
14 rows in set (0.01 sec)

2、REPLACE() function

Replace some characters in a string with other characters .

The syntax is as follows ：

--  hold  str1  Medium  str2  Substring is replaced with  str3  Substring 
--  If the position of the string to be replaced is determined , I don't know the content , Use  INSERT()  function 
--  If the content of the string to be replaced is determined , The location is uncertain , Use  REPLACE()  function 
REPLACE(str1,str2,str3)

for example ： hold s_name Medium 【 Hua 】 Replace the word with Pinyin 【HUA】

mysql> select s_id, s_name, replace(s_name, ' Hua ', 'HUA') name2 from student;
+-------+-----------+-----------+
| s_id  | s_name    | name2     |
+-------+-----------+-----------+
| S2011 |  Zhang Xiaogang     |  Zhang Xiaogang     |
| S2012 |  Liu Xiaoqing     |  Liu Xiaoqing     |
| S2013 |  Cao mengde     |  Cao mengde     |
| S2014 |  Liu Yan       |  Liu Yan       |
| S2015 |  Liu Yan       |  Liu Yan       |
| S2016 |  Liu Ruofei     |  Liu Ruofei     |
| S2021 |  Dong Wenhua     |  Dong Wenhua     |
| S2022 |  Zhou Huajian     |  Zhou HUA build    |
| S2023 |  trump     |  trump     |
| S2024 |  Obama     |  Obama     |
| S2025 |  Zhou Jianhua     |  Zhou Jian HUA   |
| S2026 |  Zhang Xueyou     |  Zhang Xueyou     |
| S2031 |  Lee Myung Bak     |  Lee Myung Bak     |
| S2032 |  Vinci     |  Vinci     |
+-------+-----------+-----------+
14 rows in set (0.03 sec)

6、 ... and 、 Case conversion function

MySQL Four case conversion functions are provided .

The syntax is as follows ：

-- UCASE  and  UPPER  You can convert the letters in the string to uppercase letters 
-- LCASE  and  LOWER  You can convert the letters in the string to lowercase letters .
--  Non alphabetic does not convert 
LCASE(str)
UCASE(str)
LOWER(str)
UPPER(str)

for example ：

mysql> select @str := 'I am a Student123.';
+------------------------------+
| @str := 'I am a Student123.' |
+------------------------------+
| I am a Student123.           |
+------------------------------+
1 row in set (0.00 sec)

mysql> select UCASE(@str), UPPER(@str) from dual;
+--------------------+--------------------+
| UCASE(@str)        | UPPER(@str)        |
+--------------------+--------------------+
| I AM A STUDENT123. | I AM A STUDENT123. |
+--------------------+--------------------+
1 row in set (0.00 sec)

mysql> select LCASE(@str), LOWER(@str) from dual;
+--------------------+--------------------+
| LCASE(@str)        | LOWER(@str)        |
+--------------------+--------------------+
| i am a student123. | i am a student123. |
+--------------------+--------------------+
1 row in set (0.00 sec)

7、 ... and 、 Intercept substring function

This kind of function can intercept a substring from a string .

The syntax is as follows ：

LEFT(str,n)          --  Intercept from the front of the string  n  Character and return 
RIGHT(str,n)         --  Intercept from the rightmost end of the string  n  Character and return 
SUBSTR(str,m,n)      --  From  m  Character start , Intercept  n  Character and return 
SUBSTRING(str,m,n)   --  From  m  Character start , Intercept  n  Character and return 

for example ：

（1） Show phone The last four

mysql> select s_id,s_name,phone,right(phone,4) phone22 from student;
+-------+-----------+-------------+---------+
| s_id  | s_name    | phone       | phone22 |
+-------+-----------+-------------+---------+
| S2011 |  Zhang Xiaogang     | 13163735775 | 5775    |
| S2012 |  Liu Xiaoqing     | 13603732255 | 2255    |
| S2013 |  Cao mengde     | 13853735522 | 5522    |
| S2014 |  Liu Yan       | 13623735335 | 5335    |
| S2015 |  Liu Yan       | 13813735225 | 5225    |
| S2016 |  Liu Ruofei     | 13683735533 | 5533    |
| S2021 |  Dong Wenhua     | 13533735564 | 5564    |
| S2022 |  Zhou Huajian     | 13243735578 | 5578    |
| S2023 |  trump     | 13343735588 | 5588    |
| S2024 |  Obama     | 13843735885 | 5885    |
| S2025 |  Zhou Jianhua     | 13788736655 | 6655    |
| S2026 |  Zhang Xueyou     | 13743735566 | 5566    |
| S2031 |  Lee Myung Bak     | 13643732222 | 2222    |
| S2032 |  Vinci     | 13043731234 | 1234    |
+-------+-----------+-------------+---------+
14 rows in set (0.00 sec)

（2） Ask the students 【 What's your last name 】

mysql> select s_id,s_name,left(s_name,1) name22 from student;
+-------+-----------+--------+
| s_id  | s_name    | name22 |
+-------+-----------+--------+
| S2011 |  Zhang Xiaogang     |  Zhang      |
| S2012 |  Liu Xiaoqing     |  Liu      |
| S2013 |  Cao mengde     |  Cao      |
| S2014 |  Liu Yan       |  Liu      |
| S2015 |  Liu Yan       |  Liu      |
| S2016 |  Liu Ruofei     |  Liu      |
| S2021 |  Dong Wenhua     |  Dong      |
| S2022 |  Zhou Huajian     |  Zhou      |
| S2023 |  trump     |  ,      |
| S2024 |  Obama     |  Mr.      |
| S2025 |  Zhou Jianhua     |  Zhou      |
| S2026 |  Zhang Xueyou     |  Zhang      |
| S2031 |  Lee Myung Bak     |  Li      |
| S2032 |  Vinci     |  reach      |
+-------+-----------+--------+
14 rows in set (0.00 sec)

（3） Show phone Of the 4 To the first 7 position

mysql> select s_id,s_name,phone,substr(phone,4,4) phone22 from student;
+-------+-----------+-------------+---------+
| s_id  | s_name    | phone       | phone22 |
+-------+-----------+-------------+---------+
| S2011 |  Zhang Xiaogang     | 13163735775 | 6373    |
| S2012 |  Liu Xiaoqing     | 13603732255 | 0373    |
| S2013 |  Cao mengde     | 13853735522 | 5373    |
| S2014 |  Liu Yan       | 13623735335 | 2373    |
| S2015 |  Liu Yan       | 13813735225 | 1373    |
| S2016 |  Liu Ruofei     | 13683735533 | 8373    |
| S2021 |  Dong Wenhua     | 13533735564 | 3373    |
| S2022 |  Zhou Huajian     | 13243735578 | 4373    |
| S2023 |  trump     | 13343735588 | 4373    |
| S2024 |  Obama     | 13843735885 | 4373    |
| S2025 |  Zhou Jianhua     | 13788736655 | 8873    |
| S2026 |  Zhang Xueyou     | 13743735566 | 4373    |
| S2031 |  Lee Myung Bak     | 13643732222 | 4373    |
| S2032 |  Vinci     | 13043731234 | 4373    |
+-------+-----------+-------------+---------+
14 rows in set (0.00 sec)

8、 ... and 、 Find substring function

1、LOCATE() function

Find where a string appears in another string .

The syntax is as follows ：

--  If  str1  yes  str2  Substring of , Then return the position where the substring first appears , Otherwise return to 0
LOCATE(str1, str2)

for example ： Find a phone number that contains 5566 Student information

--  Use wildcards 
mysql> select * from student where phone like '%5566%';
+-------+-----------+--------+---------------------+-------------+-----------+
| s_id  | s_name    | gender | birth               | phone       | addr      |
+-------+-----------+--------+---------------------+-------------+-----------+
| S2026 |  Zhang Xueyou     |  male      | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |
+-------+-----------+--------+---------------------+-------------+-----------+
1 row in set (0.00 sec)

--  Use  locate()  function 
mysql> select *,locate('5566',phone) position from student where locate('5566',phone)>0;
+-------+-----------+--------+---------------------+-------------+-----------+----------+
| s_id  | s_name    | gender | birth               | phone       | addr      | position |
+-------+-----------+--------+---------------------+-------------+-----------+----------+
| S2026 |  Zhang Xueyou     |  male      | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |        8 |
+-------+-----------+--------+---------------------+-------------+-----------+----------+
1 row in set (0.02 sec)

2、POSITION() function

Find where a string appears in another string .

The syntax is as follows ：

--  If  str1  yes  str2  Substring of , Then return the position where the substring first appears , Otherwise return to 0
-- LOCATE  Functions and  POSTION  The function uses the same , The difference is  LOCATE  The two parameters of the function are separated by commas ,POSITION  The two parameters of the function are  in  separate 
POSITION(str1 in str2)

for example ： Find a phone number that contains 55 Student information

--  Use wildcards 
mysql> select * from student where phone like '%55%';
+-------+-----------+--------+---------------------+-------------+-----------+
| s_id  | s_name    | gender | birth               | phone       | addr      |
+-------+-----------+--------+---------------------+-------------+-----------+
| S2012 |  Liu Xiaoqing     |  Woman      | 1999-10-11 00:00:00 | 13603732255 |  Xinxiang City     |
| S2013 |  Cao mengde     |  male      | 1998-02-13 00:00:00 | 13853735522 |  Zhengzhou city     |
| S2016 |  Liu Ruofei     |  Woman      | 2000-08-31 00:00:00 | 13683735533 |  Kaifeng City     |
| S2021 |  Dong Wenhua     |  Woman      | 2000-07-30 00:00:00 | 13533735564 |  Kaifeng City     |
| S2022 |  Zhou Huajian     |  male      | 1999-05-25 00:00:00 | 13243735578 |  Zhengzhou city     |
| S2023 |  trump     |  male      | 1999-06-21 00:00:00 | 13343735588 |  Xinxiang City     |
| S2025 |  Zhou Jianhua     |  male      | 2000-08-22 00:00:00 | 13788736655 |  Kaifeng City     |
| S2026 |  Zhang Xueyou     |  male      | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |
+-------+-----------+--------+---------------------+-------------+-----------+
8 rows in set (0.00 sec)

--  Use  position()  function 
mysql> select *,position('55' in phone) position from student where position('55' in phone)>0;
+-------+-----------+--------+---------------------+-------------+-----------+----------+
| s_id  | s_name    | gender | birth               | phone       | addr      | position |
+-------+-----------+--------+---------------------+-------------+-----------+----------+
| S2012 |  Liu Xiaoqing     |  Woman      | 1999-10-11 00:00:00 | 13603732255 |  Xinxiang City     |       10 |
| S2013 |  Cao mengde     |  male      | 1998-02-13 00:00:00 | 13853735522 |  Zhengzhou city     |        8 |
| S2016 |  Liu Ruofei     |  Woman      | 2000-08-31 00:00:00 | 13683735533 |  Kaifeng City     |        8 |
| S2021 |  Dong Wenhua     |  Woman      | 2000-07-30 00:00:00 | 13533735564 |  Kaifeng City     |        8 |
| S2022 |  Zhou Huajian     |  male      | 1999-05-25 00:00:00 | 13243735578 |  Zhengzhou city     |        8 |
| S2023 |  trump     |  male      | 1999-06-21 00:00:00 | 13343735588 |  Xinxiang City     |        8 |
| S2025 |  Zhou Jianhua     |  male      | 2000-08-22 00:00:00 | 13788736655 |  Kaifeng City     |       10 |
| S2026 |  Zhang Xueyou     |  male      | 1998-07-06 00:00:00 | 13743735566 |  Zhengzhou city     |        8 |
+-------+-----------+--------+---------------------+-------------+-----------+----------+
8 rows in set (0.00 sec)

Nine 、 Other functions

1、BIN() function

Convert an integer into a binary number , The type of the returned result is string .

The syntax is as follows ：

--  The argument is an integer , If the parameter is decimal , Then it will be rounded before processing 
--  Put the number  n  Convert to binary form , The return value is a function of  0  and  1  Composed string 
BIN(n)

for example ：

mysql> select bin(101),bin(2.89) from dual;
+----------+-----------+
| bin(101) | bin(2.89) |
+----------+-----------+
| 1100101  | 10        |
+----------+-----------+
1 row in set (0.03 sec)

2、FORMAT() function

Round a value and return , The type of the returned result is string .

The syntax is as follows ：

--  For the value  x  Perform rounding operation , Retain  d  Is a decimal , The return value is a string 
--  The function and  ROUND()  Function similar to , Only the types of return values are different 
ORMAT(x,d)

for example ：

mysql> select format(25.1258,2),format(1254.2,-1) from dual;
+-------------------+-------------------+
| format(25.1258,2) | format(1254.2,-1) |
+-------------------+-------------------+
| 25.13             | 1,254             |
+-------------------+-------------------+
1 row in set (0.02 sec)

3、REPEAT() function

Generate a string repeated by n A string composed of times .

The syntax is as follows ：

--  Generate a  n  individual  str  Connected string 
REPEAT(str,n)

for example ：

mysql> select repeat('abc',4),repeat(' Wang Peng ',3) from dual;
+-----------------+--------------------+
| repeat('abc',4) | repeat(' Wang Peng ',3)   |
+-----------------+--------------------+
| abcabcabcabc    |  Wang Peng, Wang Peng, Wang Peng        |
+-----------------+--------------------+
1 row in set (0.00 sec)

mysql> select concat(s_id,repeat('=',4),'>',s_name) from student;
+---------------------------------------+
| concat(s_id,repeat('=',4),'>',s_name) |
+---------------------------------------+
| S2011====> Zhang Xiaogang                       |
| S2012====> Liu Xiaoqing                       |
| S2013====> Cao mengde                       |
| S2014====> Liu Yan                         |
| S2015====> Liu Yan                         |
| S2016====> Liu Ruofei                       |
| S2021====> Dong Wenhua                       |
| S2022====> Zhou Huajian                       |
| S2023====> trump                       |
| S2024====> Obama                       |
| S2025====> Zhou Jianhua                       |
| S2026====> Zhang Xueyou                       |
| S2031====> Lee Myung Bak                       |
| S2032====> Vinci                       |
+---------------------------------------+
14 rows in set (0.00 sec)

4、SPACE() function

Generate a string consisting of several spaces .

The syntax is as follows ：

--  Return from  n  A string of spaces 
SPACE(n)

for example ：

mysql> select concat(s_id,space(6),s_name) from student;
+------------------------------+
| concat(s_id,space(6),s_name) |
+------------------------------+
| S2011       Zhang Xiaogang             |
| S2012       Liu Xiaoqing             |
| S2013       Cao mengde             |
| S2014       Liu Yan               |
| S2015       Liu Yan               |
| S2016       Liu Ruofei             |
| S2021       Dong Wenhua             |
| S2022       Zhou Huajian             |
| S2023       trump             |
| S2024       Obama             |
| S2025       Zhou Jianhua             |
| S2026       Zhang Xueyou             |
| S2031       Lee Myung Bak             |
| S2032       Vinci             |
+------------------------------+
14 rows in set (0.00 sec)

5、REVERSE() function

Flip the contents of a string .

The syntax is as follows ：

--  return str The flip string of 
REVERSE(str)

for example ：

mysql> select s_id, s_name, reverse(s_name) from student;
+-------+-----------+-----------------+
| s_id  | s_name    | reverse(s_name) |
+-------+-----------+-----------------+
| S2011 |  Zhang Xiaogang     |  Just Xiao Zhang           |
| S2012 |  Liu Xiaoqing     |  Qing Xiaoliu           |
| S2013 |  Cao mengde     |  De mengcao           |
| S2014 |  Liu Yan       |  Yanliu             |
| S2015 |  Liu Yan       |  Yanliu             |
| S2016 |  Liu Ruofei     |  Fei Ruo Liu           |
| S2021 |  Dong Wenhua     |  Hua Wendong           |
| S2022 |  Zhou Huajian     |  Jianhua week           |
| S2023 |  trump     |  Prant           |
| S2024 |  Obama     |  Mabao           |
| S2025 |  Zhou Jianhua     |  Hua Jianzhou           |
| S2026 |  Zhang Xueyou     |  There is Zhang           |
| S2031 |  Lee Myung Bak     |  Bo Ming Li           |
| S2032 |  Vinci     |  Chifanda           |
+-------+-----------+-----------------+
14 rows in set (0.00 sec)

6、STRCMP() function

Compare the size of two strings .

The syntax is as follows ：

--  According to the rules of comparison , If the string  str1  Greater than  str2, return  1
--  If the string  str1  Less than  str2, return  -1
--  If the string  str1  and  str2  Exactly the same , Then return to  0
STRCMP(str1,str2)

for example ：

mysql> select strcmp('abc','abc'),strcmp('abc','bcd'),strcmp('abc','123') from dual;
+---------------------+---------------------+---------------------+
| strcmp('abc','abc') | strcmp('abc','bcd') | strcmp('abc','123') |
+---------------------+---------------------+---------------------+
|                   0 |                  -1 |                   1 |
+---------------------+---------------------+---------------------+
1 row in set (0.00 sec)

7、SUBSTRING_INDEX() function

The syntax is as follows ：

--  If  n  Greater than  0, Returns the number from the left  n  individual  delimiter  All contents to the left of the character represented 
--  If  n  Less than  0, Return the number from the right  n  individual  delimiter  All contents to the right of the character represented 
SUBSTRING_INDEX(str,delimiter,n)

for example ： There is the following table pic.

/* create table pic(id int primary key,name char(20),file varchar(200)); insert into pic values(1,'flower','c:\\mydoc\\picture\\flower.jpg'); insert into pic values(2,'sun','d:\\camera\\picture\\sun.png'); insert into pic values(3,'spring','d:\\camera\\pic\\spring.psd'); insert into pic values(4,'moon','e:\\history\\2011-3-22\\moon.jpg'); insert into pic values(5,'school','e:\\history\\2020-12-3\\school.jpg'); */
mysql> select * from pic;
+----+--------+---------------------------------+
| id | name   | file                            |
+----+--------+---------------------------------+
|  1 | flower | c:\mydoc\picture\flower.jpg     |
|  2 | sun    | d:\camera\picture\sun.png       |
|  3 | spring | d:\camera\pic\spring.psd        |
|  4 | moon   | e:\history\2011-3-22\moon.jpg   |
|  5 | school | e:\history\2020-12-3\school.jpg |
+----+--------+---------------------------------+
5 rows in set (0.00 sec)

（1） The extension of the file in the query table

mysql> select *,substring_index(file,'.',-1) from pic;
+----+--------+---------------------------------+------------------------------+
| id | name   | file                            | substring_index(file,'.',-1) |
+----+--------+---------------------------------+------------------------------+
|  1 | flower | c:\mydoc\picture\flower.jpg     | jpg                          |
|  2 | sun    | d:\camera\picture\sun.png       | png                          |
|  3 | spring | d:\camera\pic\spring.psd        | psd                          |
|  4 | moon   | e:\history\2011-3-22\moon.jpg   | jpg                          |
|  5 | school | e:\history\2020-12-3\school.jpg | jpg                          |
+----+--------+---------------------------------+------------------------------+
5 rows in set (0.00 sec)

（2） Query the file name in the table （ No path ）

mysql> select *,substring_index(file,'\\',-1) from pic;
+----+--------+---------------------------------+-------------------------------+
| id | name   | file                            | substring_index(file,'\\',-1) |
+----+--------+---------------------------------+-------------------------------+
|  1 | flower | c:\mydoc\picture\flower.jpg     | flower.jpg                    |
|  2 | sun    | d:\camera\picture\sun.png       | sun.png                       |
|  3 | spring | d:\camera\pic\spring.psd        | spring.psd                    |
|  4 | moon   | e:\history\2011-3-22\moon.jpg   | moon.jpg                      |
|  5 | school | e:\history\2020-12-3\school.jpg | school.jpg                    |
+----+--------+---------------------------------+-------------------------------+
5 rows in set (0.00 sec)

（3） Query the file path in the table

/* select *, left(file,char_length(file)-char_length(substring_index(file,'\\',-1))) path from pic; */
mysql> select *,
    -> left(file,char_length(file)-char_length(substring_index(file,'\\',-1))) path 
    -> from pic;
+----+--------+---------------------------------+-----------------------+
| id | name   | file                            | path                  |
+----+--------+---------------------------------+-----------------------+
|  1 | flower | c:\mydoc\picture\flower.jpg     | c:\mydoc\picture\     |
|  2 | sun    | d:\camera\picture\sun.png       | d:\camera\picture\    |
|  3 | spring | d:\camera\pic\spring.psd        | d:\camera\pic\        |
|  4 | moon   | e:\history\2011-3-22\moon.jpg   | e:\history\2011-3-22\ |
|  5 | school | e:\history\2020-12-3\school.jpg | e:\history\2020-12-3\ |
+----+--------+---------------------------------+-----------------------+
5 rows in set (0.00 sec)

（4） Query the drive letter of the file in the table

mysql> select *,substring_index(file,'\\',1) from pic;
+----+--------+---------------------------------+------------------------------+
| id | name   | file                            | substring_index(file,'\\',1) |
+----+--------+---------------------------------+------------------------------+
|  1 | flower | c:\mydoc\picture\flower.jpg     | c:                           |
|  2 | sun    | d:\camera\picture\sun.png       | d:                           |
|  3 | spring | d:\camera\pic\spring.psd        | d:                           |
|  4 | moon   | e:\history\2011-3-22\moon.jpg   | e:                           |
|  5 | school | e:\history\2020-12-3\school.jpg | e:                           |
+----+--------+---------------------------------+------------------------------+
5 rows in set (0.00 sec)

8、LPAD() And RPAD() function

LPAD() And RPAD() Function fills several characters in the front or back of a string , Make the string reach the specified length .

The syntax is as follows ：

--  Put the string  str  use  padstr  The string is filled to a length of  len, And returns a length of  len  String 
-- LPAD  function  str  String right justified ,padstr  Fill in from the left 
-- RPAD  function  str  String left justified ,padstr  Fill from the right end 
LPAD(str, len, padstr)
RPAD(str, len, padstr)

for example ：

mysql> select id,concat(name,'||',file) from pic;
+----+-----------------------------------------+
| id | concat(name,'||',file)                  |
+----+-----------------------------------------+
|  1 | flower||c:\mydoc\picture\flower.jpg     |
|  2 | sun||d:\camera\picture\sun.png          |
|  3 | spring||d:\camera\pic\spring.psd        |
|  4 | moon||e:\history\2011-3-22\moon.jpg     |
|  5 | school||e:\history\2020-12-3\school.jpg |
+----+-----------------------------------------+
5 rows in set (0.00 sec)

-- rpad()  function ： Align left , Fill in space on the right 
mysql> select id,concat(rpad(name,8,' '),'||',file) from pic;
+----+-------------------------------------------+
| id | concat(rpad(name,8,' '),'||',file)        |
+----+-------------------------------------------+
|  1 | flower  ||c:\mydoc\picture\flower.jpg     |
|  2 | sun     ||d:\camera\picture\sun.png       |
|  3 | spring  ||d:\camera\pic\spring.psd        |
|  4 | moon    ||e:\history\2011-3-22\moon.jpg   |
|  5 | school  ||e:\history\2020-12-3\school.jpg |
+----+-------------------------------------------+
5 rows in set (0.00 sec)

-- lpad()  function ： Right alignment , Fill in the space on the left 
mysql> select id,concat(rpad(name,8,' '),'||',lpad(file,35,' ')) from pic;
+----+-------------------------------------------------+
| id | concat(rpad(name,8,' '),'||',lpad(file,35,' ')) |
+----+-------------------------------------------------+
|  1 | flower  ||        c:\mydoc\picture\flower.jpg   |
|  2 | sun     ||          d:\camera\picture\sun.png   |
|  3 | spring  ||           d:\camera\pic\spring.psd   |
|  4 | moon    ||      e:\history\2011-3-22\moon.jpg   |
|  5 | school  ||    e:\history\2020-12-3\school.jpg   |
+----+-------------------------------------------------+
5 rows in set (0.00 sec)