MySQL notes
MySQL isn't my first choice of database, but it isn't a bad choice either. I prefer PostgreSQL, but everyone uses MySQL.
Contents
~/.my.cnf
[mysql] database = my_favorite_database user = noah password = ze_zecret_passwort host = localhost auto-rehash=true i-am-a-dummy
Create a user
This creates a new root level user named USERNAME with no password.
$ mysql -u root -e "GRANT ALL ON *.* to USERNAME@localhost;" $ mysql -u root -e "GRANT ALL ON *.* to USERNAME@'%';"
This creates a new user with a password.
$ mysql -u root -e "GRANT ALL ON *.* to USERNAME@localhost IDENTIFIED BY 'some_pass' WITH GRANT OPTION;" $ mysql -u root -e "GRANT ALL ON *.* to USERNAME@'%' IDENTIFIED BY 'some_pass' WITH GRANT OPTION;"
Error mixing old MySQL client with newer MySQL server
If you are using an old MySQL client to connect to a later version of MySQL you may get an error:
Client does not support authentication protocol requested by server; consider upgrading MySQL client
This happens when using a MySQL client prior to version 4.1 with a server later than version 4.1. The best thing to do is to upgrade the client. If that cannot be done then set the password on the server to use the old password hash:
SET PASSWORD FOR 'USERNAME'@'some_host' = OLD_PASSWORD('some_pass');
lost root password
Stop mysql server.
/etc/init.d/mysql stop
Edit /etc/my.cnf or /etc/mysql/my.cnf and add this line anywhere after the [mysqld] section:
skip-grant-tables
Start mysql server:
/etc/init.d/mysql start
Now you can connect without a password. Grant commands won't work. You can reset the password by directly updating the User table:
mysql> use mysql mysql> update mysql.user set Password=password('newpassword') where User='root';
Remove skip-grant-tables from /etc/my.cnf.
Restart mysql server:
/etc/init.d/mysql restart
select into file
I always forget this:
SELECT * FROM foo INTO OUTFILE '/tmp/foo.sql';
select into CSV file
SELECT * FROM foo INTO OUTFILE '/tmp/foo.csv' FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n';
load table from file
LOAD DATA INFILE '/tmp/foo.csv' INTO TABLE foo FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n';
It is pretty easy to read directly from MySQL memmapped files. This can be handy when you need to hack a search through data files rather than doing a proper query. Sometimes it's faster to dump data this way.
#!/usr/bin/env python import mmap import os, sys, string def hex_filter (b, offset, block_size = 8): """Any unprintable characters are converted to line feeds, but only one line feed is printed per cluster of unprintable characters. """ unprintable_flag = True # used to track unprintable chunk state. for i in xrange (offset, offset+block_size): #if b[i] in string.printable: if ord(b[i])>=ord(' ') and ord(b[i])<=ord('~'): sys.stdout.write("%s"%b[i]) unprintable_flag = False else: if not unprintable_flag: sys.stdout.write("\n") unprintable_flag = True def main (): filename="/var/lib/mysql/var/test/rmscrub.MYI" file = open(filename, "rb") size = os.path.getsize(filename) data = mmap.mmap(file.fileno(), size, access=mmap.ACCESS_READ) print "Note that 'data' is a memmapped file and 'size' is taken from the memmapped file size," print "so len(data) and size should be the same:" print "len(data):", len(data) print "size: ", size block_size = 2048 size = 1000000 for i in xrange(0,size, block_size): hex_filter(data,i, block_size) main()