Built in functions other functions

11.12　MySQL Other functions of

MySQL There are some functions in that cannot be specifically classified , But these functions are MySQL It can not be ignored in the process of development, operation and maintenance , This section briefly introduces MySQL Functions that cannot be specifically classified in .

11.12.1　FORMAT(value,n) function

FORMAT(value,n) Function returns a pair of numbers value Formatted result data , among n It means to keep it after the decimal point after rounding n position . If n Is less than or equal to 0, Then only the integer part .

---

mysql> SELECT FORMAT(123.123, 2), FORMAT(123.523, 0), FORMAT(123.123, -2); +--------------------+--------------------+---------------------+| FORMAT(123.123, 2) | FORMAT(123.523, 0) | FORMAT(123.123, -2) |+--------------------+--------------------+---------------------+| 123.12             | 124                | 123                 |+--------------------+--------------------+---------------------+1 row in set (0.00 sec)

---

11.12.2　CONV(value,from,to) function

CONV(value,from,to) Function will value The value of is converted between different hexadecimals ,value It's an integer , If any of the parameters is NULL, The result returns NULL. An example is as follows ：

---

mysql> SELECT CONV(16, 10, 2), CONV(8888,10,16), CONV(NULL, 10, 2);+-----------------+------------------+-------------------+| CONV(16, 10, 2) | CONV(8888,10,16) | CONV(NULL, 10, 2) |+-----------------+------------------+-------------------+| 10000           | 22B8             | NULL              |+-----------------+------------------+-------------------+1 row in set (0.00 sec)

---

11.12.3　INET_ATON(value) function

INET_ATON(value) Functions will be separated by dots IP The address is converted into a number , among ,value Is represented by dots IP Address . An example is as follows ：

---

mysql> SELECT INET_ATON('192.168.1.100');+----------------------------+| INET_ATON('192.168.1.100') |+----------------------------+|                 3232235876 |+----------------------------+1 row in set (0.00 sec)

---

With “192.168.1.100” For example , The calculation method is 192 multiply 256 Of 3 Power , add 168 multiply 256 Of 2 Power , add 1 multiply 256, Plus 100.

11.12.4　INET_NTOA(value) function

INET_NTOA(value) Function will be in numerical form IP The address is converted to dot separated IP Address . An example is as follows ：

---

mysql> SELECT INET_NTOA(3232235876);+-----------------------+| INET_NTOA(3232235876) |+-----------------------+| 192.168.1.100         |+-----------------------+1 row in set (0.00 sec)

---

You can see ,INET_ATON(value) Function and INET_NTOA(value) Functions are inverse functions to each other .

11.12.5　BENCHMARK(n,expr) function

BENCHMARK(n,expr) Function will express expr repeat n Time , Mainly used for testing MySQL Handle expr The time taken by the expression . An example is as follows ：

---

mysql> SELECT BENCHMARK(1, MD5('mysql'));+----------------------------+| BENCHMARK(1, MD5('mysql')) |+----------------------------+|                          0 |+----------------------------+1 row in set (0.00 sec)

---

You can see , The string mysql perform 1 Time MD5 Encryption takes little time .

---

mysql> SELECT BENCHMARK(1000000, MD5('mysql')); +----------------------------------+| BENCHMARK(1000000, MD5('mysql')) |+----------------------------------+|                                0 |+----------------------------------+1 row in set (0.20 sec)

---

You can see , The string mysql perform 1000000 Time MD5 Encryption takes time 0.20s.

11.12.6　CAST(value AS type) function

CAST(value AS type) Function will value Convert to type Type value , among type The values of are shown in the table 11-6 Shown .

surface 11-6　CAST(value AS type) Function type Desirable value

An example is as follows ：

---

mysql> SELECT CAST('123' AS SIGNED);+-----------------------+| CAST('123' AS SIGNED) |+-----------------------+|                   123 |+-----------------------+1 row in set (0.00 sec)

---

CONVERT(value,type) Functions and CAST(value AS type) The same function , I won't repeat .

11.12.7　CONVERT(value USING char_code) function

take value The character encoding used is modified to char_code, An example is as follows ：

---

mysql> SELECT CHARSET('mysql'), CHARSET(CONVERT('mysql' USING 'utf8'));+------------------+----------------------------------------+| CHARSET('mysql') | CHARSET(CONVERT('mysql' USING 'utf8')) |+------------------+----------------------------------------+| utf8mb4          | utf8                                   |+------------------+----------------------------------------+1 row in set, 1 warning (0.00 sec)

---

You can see ,MySQL The default character encoding for strings is utf8mb4, have access to CONVERT(value USING char_code) Function to change it to UTF-8.