MySQL

Reseeding a table in SQL Server... (Reset the identity column)

Kyle — Wed, 01 Aug 2007 08:39:05 GMT

DBCC CHECKIDENT('tablename', RESEED, 1)

Hierarchical Data Followup

Kyle — Wed, 15 Feb 2006 04:47:00 GMT

Back in November, I posted about a Hierarchical Data scheme that I was working on for a category tree. The article I mentioned came in handy.

Well, I'm working on another project (this time, it's a project for my wife), but wanted the possibility of multiple users defining their own hierarchical tree, but store them all in the same table. This is using the Nested Set model.

The table will look like:

+-------------+---------------+
| Name        | char(255)     |
| lft         | int           |
| rgt         | int           |
| Owner       | char(255)     |
+-------------+---------------+

The owner field will keep track of the multiple users.

+-------------+---+---+-------+
| Name        |lft|rgt|owner  |
+-------------+---+---+-------+
| Root        | 1 | 4 | kyle |
| Category1   | 2 | 3 | kyle |
| Root        | 1 | 4 | kyle1 |
| Category12 | 2 | 3 | kyle1 |
+-------------+---+---+-------+

Now, the query to pull back the data, with the depths...

SELECT node.*, (COUNT(parent.name) - 1) AS depth
FROM table1 AS node,
table1 AS parent
WHERE node.lft BETWEEN parent.lft AND parent.rgt
GROUP BY node.name
ORDER BY node.lft;

This may bring back all the correct information, but the depths will be screwed up. I'm not sure of all the technical details behind that, and it's something that I want to learn. But, I did figure out how to fix this.

SELECT node.name, (COUNT(parent.name) - 1) AS depth
FROM (select * from table1 where owner = 'kyle') AS node,
(select * from table1 where owner = 'kyle') AS parent
WHERE node.lft BETWEEN parent.lft AND parent.rgt
GROUP BY node.name
ORDER BY node.lft;

The calculations are based off of a base table, which is in the first query defined as table1. This is the entire dataset. However, if we narrow the data down to only the data requested for each user by defining a select query in the from statement, it "tricks" the join into thinking that the data subset is the table.

I'm sure this last paragraph was as clear as mud, but you get the point. With this model, you can do multiple nested data sets inside of one table. Great for a shared environment.

Flash and XML

Kyle — Tue, 20 Dec 2005 03:06:00 GMT

I'm not much of a PHP guy. In fact, I avoid it whenever I can. But, my church is hosting their website on a great linux provider, which has provided great service for us for the past few years. The linux server uses ChiliSoft ASP (apparently now owned by Sun... That's interesting), which also is a nifty little implementation of ASP for linux.

The only problem is, every six months or so, the ASP service on the linux box hangs. Not a big deal, I just fire off a little e-mail to the help desk, and they have it back up and running. That is, if I check every day. Since I'm a forgetful webmaster, I don't, and sometimes these things go unnoticed. Plus, now that we've jumped in traffic since offering podcasting, we can't really afford to have the site go down.

Well, it's time for an overhaul. The site hasn't been touched in 3 or 4 years. Yes, we've made minor improvements, but it's time for a complete overhaul. So, after working with the staff, as well as the graphic designer in our congregation, we have an awesome looking site. I even put it into Flash. Dynamic XML and all. So, the site has a 58k footprint (awesome for dial-up), and only about 2 k of text loads for each page (if that). Incredible. Fast, etc. SWEET.

Well, to get the data in and out from the DB, I didn't want to rely on the slightly unreliable ASP, so I decided to write the data layer in PHP. It's Picky. That's all I have to say. Makes me thankful that I'm not a C# programmer (case sensitivity).

Anyway. I'll post when the site is finished. Should be "live" around January 8th.

MySQL Membership Provider

Kyle — Thu, 15 Dec 2005 03:22:00 GMT

Here's a great article with a MySQL Membership provider.

http://www.codeproject.com/aspnet/MySQLMembershipProvider.asp

Works like a charm.

Looping through Nested Category Collections

Kyle — Thu, 10 Nov 2005 02:17:00 GMT

Recursively looping through category collection with a sub category collection.

Dim cl As New CategoryList
cl = Category.GetChildCategories(1)

Dim c As New Category
Dim cc As New Category

For Each c In cl
GetChildren(c)
Next

Function GetChildren(ByVal c As Category) As String

    Response.Write(c.Name & "<BR>")

    Dim cc As New Category

    If c.ChildCategories.Count > 0 Then
        For Each cc In c.ChildCategories
            GetChildren(cc)
        Next
    End If

End Function

Building a category tree.

Kyle — Wed, 09 Nov 2005 20:13:00 GMT

In my last post, I mentioned an article that deals with Nested Set Heirarchical data in MySQL. I'm at this point trying to design a business layer / data layer class around the concepts in this article.

I've run into a big wall in trying to develop a scheme in which I can get the most amount of data into the class with the fewest amount of hits to the database. The other problem is that I'd not only like my data to be heirarchical, but the objects in my class as well. Maybe that's wishful thinking.

I've got my solution for simple category navigation. But, I've got to come up with something else for category maps.

Hierarchical Data in MySQL

Kyle — Tue, 08 Nov 2005 21:49:00 GMT

There's a really good article over on dev.mysql.com by Mike Hillyer that deals with Hierarchical Data in MySQL. This is particularly helpful for category structures, and aggregating categories and counts of items in categories. It's a very comprehensive article, providing sample code for almost any scenario where aggregating data is necessary.

Very nice.

MySQL Connector/.NET & Like

Kyle — Mon, 07 Nov 2005 20:20:00 GMT

With the MySQL Connector/.NET, parameterized queries are performed like this:
dim sql as string = "SELECT * FROM table1 WHERE field1 = ?field1"

cmd.Parameters.Add("?field1", "Value")

Great. What about LIKE statements?

dim sql as string = "SELECT * FROM table1 WHERE field1 like ?field1"

cmd.Parameters.Add("?field1", "Value")

The only way I've gotten this to work is:

dim sql as string = "SELECT * FROM table1 WHERE value1 like ?value1"

cmd.Parameters.add("?value1", "%Value%")

Am I missing something?

Web App Flipping Out

Kyle Holder — Fri, 04 Nov 2005 16:38:00 GMT

I'm not sure why, but one of my sites is flipping out.

About once a day, the app hangs, and gives me an error in the emHits.save module. I'm not sure why. It's a simple class that saves a visit to the site to the DB.

I wonder if it's the ODBC connector that I'm using?... Sheesh.

K-