Database – James Lin's Blog

New technology to crack down on house-flipping

James Lin — Thu, 09 Mar 2017 20:44:22 +0000

Just read an article on cracking down house flipping in NZ, it says “New Zealand’s real estate watchdog is ramping up its crackdown on house-flipping by investing in new technology which allows it to track when properties have been quickly re-sold for huge profits.”

So what’s the new technology is about? You would have thought there is a database table with a simple SQL query like this:

select * from sales_record r1 left join sales_record r2 on r1.title_no = r2.title_no and r1.id < r2.id where datediff(r2.sales_date, r1.sales_date) < 30;

Installing Python Mysql Adapter On Mac OSX

James Lin — Mon, 11 Feb 2013 18:40:42 +0000

First download and install mysql for Mac OSX
Install virtualenv, create a virtualenv and activate it
Pip install mysql-python, and you will see an error “EnvironmentError: mysql_config not found”
Find the mysql_config by running “sudo find / -name ‘mysql_config'”
Go to your /path to virtualenv/build/mysql-python
Edit site.cfg
Uncomment this line “#mysql_config = /usr/local/bin/mysql_config” and change the path to what you found in step 4
Then run “python setup.py install”
if you get “Library not loaded: libmysqlclient.18.dylib” when using the adapter
Then symlink this file: “sudo ln -s /usr/local/mysql/lib/libmysqlclient.18.dylib /usr/lib/libmysqlclient.18.dylib”

To control the server:

sudo /Library/StartupItems/MySQLCOM/MySQLCOM stop
sudo /Library/StartupItems/MySQLCOM/MySQLCOM start
sudo /Library/StartupItems/MySQLCOM/MySQLCOM restart

MySQL locate function

James Lin — Wed, 29 Feb 2012 20:28:32 +0000

So everyone knows sql LIKE to search wildcard matches the criteria. How about in a situation that you need to return all the rows that has value is part of the criteria string.

eg. given a full URL http://www.abc.com/bl/abcdefg/, return all the rows with uri_part field that values are part of the URL string.

+------------+
|uri_part    |
+------------+
|/bl/        |
|/bl/abc/    |
|/ba/abc/    |
+------------+

Normally LIKE statement works on the other way around, so you need to use LOCATE function. So in this example would be:

SELECT uri_part FROM table WHERE locate(uri_part, 'http://www.abc.com/bl/abcdefg/');

Hash Reserve Lookup Database Just Hit 5 Million Entries

James Lin — Mon, 20 Dec 2010 02:49:35 +0000

Late last week, I started a hash reserve lookup service, and today the database has just grown over 5 million entries. By the end of this week I reckon we will 10 million entries, hopefully we can have better search result by then. Fingers crossed!

MyISAM vs InnoDB decision matrix

James Lin — Sun, 19 Dec 2010 02:10:01 +0000

Ever had problem choosing the right MySQL storage engine? Here is a simple matrix for you to make your decision

Is your table is going to be inserted, deleted, and updated much much more than it is going to be selected?	InnoDB
If you need full-text search	MyISAM
If you prefer/require relational database design	InnoDB
Is disk-space or ram an issue?	MyISAM
In Doubt?	MyISAM

reference: http://www.mikebernat.com/blog/MySQL_-_InnoDB_vs_MyISAM

Is your table is going to be inserted, deleted, and updated much much more than it is going to be selected?	InnoDB
If you need full-text search	MyISAM
If you prefer/require relational database design	InnoDB
Is disk-space or ram an issue?	MyISAM
In Doubt?	MyISAM