Allow custom column types in your Rails migrations
posted: April 7th, 2007 · by: Sven
We’ll all admit it. Rails’ migrations rock. Totally.
But when you try to change a database column to some vendor specific type (like varbinary for MySQL) that Rails doesn’t implement you notice that Rails doesn’t hand over control that easily here like it does elsewhere in ActiveRecord. You’re just not supposed to use any custom types.
This article explains how to easily change that behaviour.
Read the rest of this entryGetting MySQL compare Unicode Greek Extended characters correctly
posted: February 8th, 2007 · by: Sven
Lately I ran into an interesting issue with MySQL’s string comparsion that I haven’t seen before.
I’ve been setting up a simple vocabulary and grammar learning program for my spouse who’s started learning ancient greek a while ago. After she’s entered some testdata containing several funny looking ancient greek characters we saw that MySQL 4.1 seems to treat the following characters as equal when compared as VARCHAR:
| Char. | Unicode Codepos. |
UTF-8 | Name |
 |
U+03B7 | 206 183 | eta |
 |
U+1F75 | 225 189 181 | eta w/ oxia |
 |
U+1FC4 | 225 191 135 | eta w/ persispomeni and ypogegrammenti |
These characters are stored and retrieved correctly (which was a nice thing to watch, by the way). But when it comes to compare them to each other they are wrongly regarded the same character.
Read the rest of this entryUsing a self join to select the rows with the maxium values per group
posted: June 1st, 2006 · by: Sven
Phew. This really baffled me. I use SQL for *years* now … but I haven’t been able to come up with a working statement for a query that I’ve thought to be a really trivial thing at first.
Like this:
I have a table articles which can belong to blogs. But blogs are subclasses of an abstract type called location. Thus, each article holds a key to the table locations where there is a column type, which will have the value ‘blog’ for each concrete blog.
Read the rest of this entry