MySQL Yun Koriyuki---knowledge accumulation

First, MySQL SQL processing business class

1.1. Calculate the Age by birthday

Select Date_format (From_days (To_days (now ())-to_days (' 1788-11-26 '), '%Y ') +0;

1.2, mysqladmin command Change password,-h specifies the IP of the database server

#/usr/mysql/bin/mysqladmin-h 192.168.0.%-uyangsq-p Password
Enter Password:
/usr/mysql/bin/mysqladmin:connect to server at ' 192.168.0.% ' failed
Error: ' Unknown MySQL Server Host ' 192.168.0.% ' (2) '
Check that mysqld are running on 192.168.0.% and that the port is 3306.
You can check the this by doing ' telnet 192.168.0.% 3306 '
#/usr/mysql/bin/mysqladmin-h 192.168.0.3-uyangsq-p Password

Enter Password:
New Password:
Confirm New Password:

1.3. Close multiple servers, you must connect to the specified port number

#/usr/mysql/bin/mysqladmin--port 3306 shutdown

1.4. Add a new field name behind a field in the table

ALTER TABLE stuscore add column ClassID int not null after course;

1.5. Multiple Table association Delete multiple tables
Delete t1,t2 from class T1 inner joins Stuscore T2 on T1.classid=t2.classid and T1.classid in (for each);

1.6. The server maintains many state variables that provide information about the operation. You can reset many state variables to 0 with the flush status statement.

Show status like '%thread% ';

Threads_connected: The number of connections that are currently open.

Threads_created: Creates the number of threads used to process the connection. If the threads_created is larger, you may want to increase the thread_cache_size value. The method of calculating the cache access rate is threads_created/connections.
Threads_running: The number of active (non-sleep) threads.

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MySQL Yun Koriyuki---knowledge accumulation