What functions does MySQL have? Don't look everywhere. Just look at this.

Format function FPRMAT(x,n)

format(x,n) The digital x format , And keep the decimal point after... In the way of rounding n position , The result is returned as a string .

If n by 0, Then the return result function does not contain decimal part .

mysql> select format(999.12345678, 5), format(888.12345678, 0);
+-------------------------+-------------------------+
| format(999.12345678, 5) | format(888.12345678, 0) |
+-------------------------+-------------------------+
| 999.12346               | 888                     |
+-------------------------+-------------------------+
1 row in set (0.00 sec)

mysql>

Numbers in different base numbers are converted to each other

conv(n, from_base, to_base) This function can convert between different base numbers . For example, will 16 Conversion of decimal digits to 2 Base number , Or 2 Conversion of decimal digits to 10 It's all right .

The return value is a number n String representation of , from from_base The base number is converted to to_base Base number . If any of the parameters is null Words , So the return value is null.

mysql> select conv('a', 16, 10) as coll, conv(123, 10, 2) as coll_1, conv(123, 10, 16) as coll_2, conv(123, 10, 8) as coll_3;
+------+---------+--------+--------+
| coll | coll_1  | coll_2 | coll_3 |
+------+---------+--------+--------+
| 10   | 1111011 | 7B     | 173    |
+------+---------+--------+--------+
1 row in set (0.00 sec)

mysql>

IP Address and number conversion function

inet_auto(expr) Give a dot address representation of the network address as a string , Returns an integer representing the value of the address . The address can be 4 perhaps 8bit Address .

mysql> select inet_aton('192.168.1.1');
+--------------------------+
| inet_aton('192.168.1.1') |
+--------------------------+
|               3232235777 |
+--------------------------+
1 row in set (0.00 sec)

mysql>

conversely , We can also use inet_ntoa Function converts a numeric network address to a string network point address , To look down ：

mysql> select inet_ntoa(3232235777);
+-----------------------+
| inet_ntoa(3232235777) |
+-----------------------+
| 192.168.1.1           |
+-----------------------+
1 row in set (0.00 sec)

mysql>

therefore , From above ,inet_ntoa and inet_aton They're inverse functions to each other .

Lock function and unlock function

get_lock(str, timeout) Try to use a string str Get a lock for a given name , The timeout is timeout second . If you succeed in getting the lock , Then return to 1, If the operation times out , Then return to 0; Once an error occurs , Then return to null.

release_lock(str) Untie the quilt get_lock() Acquired 、 Use string str Lock named lock . If the lock is unlocked , Then return to 1, If the thread has not created a lock , Then return to 0（ The lock is not unlocked at this time ）; If the named lock does not exist , Then return to null. If this lock has never been get_lock() Call to get , Or the lock has been untied in advance , Then the lock does not exist .

is_free_lock(str) Check that the name is str Whether the lock can be used , If this lock can be used , Then return to 1（ No one uses this lock ）; If this lock is being used , Then return to 0; If something goes wrong , Then return to null（ Like incorrect parameters ）.

if_used_lock(str) Check that the name is str Is your lock being used , If this is locked , Returns the connection identifier of the client using the lock , Otherwise , Just go back to null.

mysql> select get_lock('yunweijia', 15) as getlock, is_used_lock('yunweijia') as isusedlock, is_free_lock('yunweijia') as isfreelock, release_lock('yunweijia') as releaselock;
+---------+------------+------------+-------------+
| getlock | isusedlock | isfreelock | releaselock |
+---------+------------+------------+-------------+
|       1 |          8 |          0 |           1 |
+---------+------------+------------+-------------+
1 row in set (0.01 sec)

mysql>

get_lock('yunweijia', 15)： The return result is 1, Description successfully got a name of ‘yunweijia’ Lock of , Duration is 15 second ;

is_used_lock('yunweijia')： The return result is the current connection id, The name is yunweijia The lock of is being used ;

is_free_lock('yunweijia')： The return is 0, The description name is yunweijia The lock of is being used ;

release_lock('yunweijia')： The return value is 1, It indicates that the unlocking is successful .

Reset the function that performs the specified operation

benchmark(count, expr) Function repetition count Number of execution expressions expr.

He can calculate with a computer mysql Speed of processing expressions . The result value is generally 0（0 It just means that the processing process is fast , Not without time ）. Another function is that it can be used in mysql The execution time of the client internal report statement .

for instance ：

First we use sha Function to encrypt a password , as follows ：

mysql> select sha('yunweijia');
+------------------------------------------+
| sha('yunweijia')                         |
+------------------------------------------+
| 683501978a90d76d420b893cd7e00c8efde8e8f3 |
+------------------------------------------+
1 row in set (0.00 sec)

mysql>

You can see from above , This article sql The execution time is 0.00 sec, Then we use benchmark function , Repeat this command 50000 Time , Look at the running time ;

mysql> select benchmark(50000, sha('yunweijia'));
+------------------------------------+
| benchmark(50000, sha('yunweijia')) |
+------------------------------------+
|                                  0 |
+------------------------------------+
1 row in set (0.03 sec)

mysql>

As you can see from the above results , It actually runs 0.03 second .

Functions that change the character set

convert(...using...)： with using Of convert() Function is used to convert data between different character sets .

mysql> select charset('yunweijia') as coll, charset(convert('yunweijia' using latin1)) as coll_1;
+---------+--------+
| coll    | coll_1 |
+---------+--------+
| utf8mb3 | latin1 |
+---------+--------+
1 row in set (0.00 sec)

mysql>

See from above , The default character set is utf8mb3, adopt convert The string yunweijia The default character set of is changed to latin1.

Functions that change data types

cast(x, as type) and convert(x, type) Function converts a value of one type to a value of another type , Convertible type There are the following ：

• binary

• char(n)

• date

• time

• datetime

• decimal

• signed

• unsigned

mysql> select cast(1000 as char(3)), convert('2022-07-18 09:09:00', time);
+-----------------------+--------------------------------------+
| cast(1000 as char(3)) | convert('2022-07-18 09:09:00', time) |
+-----------------------+--------------------------------------+
| 100                   | 09:09:00                             |
+-----------------------+--------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql>

You can see from above ,select cast(1000 as char(3)) Set integer data 1000, Convert to a string type with two display widths , The result is 100;

convert('2022-07-18 09:09:00', time) take datetime The value of type is converted to time Type values , The result is 09:09:00.

thus , In this paper, the end .

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