Database Designs: MySQL NULL Fields
Does your table designs support NULL values?
There is a debate about creating tables which permit NULL values. I personally make every effort to make every field in a table NOT NULL. The argument for this: I want to be able to depend on my SQL statements. In this post I will illustrate how an insignificant field that allows NULL values can create an issue. This is a simple illustration. More complex queries can break down as easily where NULL values are allowed.
It’s in my opinion, that NULL fields should be a topic for discussion, when you begin talking about your designs and the integrity behind those designs.
Example: NULL fields are allowed.
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CREATE TABLE SECURITY_USERS (
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SECURITY_USER_ID Integer NOT NULL,
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USER_NAME Varchar(30) NOT NULL,
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FIRST_NAME Varchar(20),
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LAST_NAME Varchar(20),
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MIDDLE_INITIAL Varchar(1),
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CONSTRAINT PK_SECURITY_USERS PRIMARY KEY (SECURITY_USER_ID),
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CONSTRAINT UNQ_SECURITY_USERS_USER_NAME UNIQUE (USER_NAME)
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) TYPE=InnoDB DEFAULT CHARSET=utf8;
There are several things wrong with this table, but for the moment I would like to simply use it as an example of a table that supports NULL values. There are plenty of other fields in this table, but I’ve removed them for the sake of this post. They all permit NULL values.
In my opinion, the problem with this style design is that “I can’t always depend on my queries to produce good results“. Most of the time the system has entered in FIRST_NAME and LAST_NAME into the table and sometimes but not always, they entered a MIDDLE_INITIAL.
So, if we have two users in the system and the data looks like this:
Example: Sample data.
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/*
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SECURITY_USER_ID | USER_NAME | LAST_NAME | FIRST_NAME | MIDDLE_INITIAL
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1 admin Master Web (NULL)
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2 jdoe Doe John B
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*/
…and one of them has a middle initial, while the other does not. Then this creates the potential for unpredictable results in advanced queries.
Example: SQL Statement.
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SELECT concat(LAST_NAME, ‘, ‘, FIRST_NAME, ‘ ‘, MIDDLE_INITIAL) AS FULL_NAME
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FROM security_users WHERE security_user_id = 1 OR security_user_id = 2
All I want to do is concatenate the users name in SQL, so it displays in the format of my choice without my having to do it in code. Sometimes, it’s nice to bring back data in the format you want. Besides, if I execute this query in more than one place in my application I don’t want to have to continue formatting it in code. I just like to have the query do it.
The problem is, when NULL fields are allowed, you cannot depend on good results. Especially if I built my query and was testing it with people who had middle names. The first time the query came across someone who had a NULL middle name in the application, the application would receive unexpected results.
Example: Query Results
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/*
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FULL_NAME
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(NULL)
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Doe, John B
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*/
Despite the fact there is data in FIRST_NAME (= Web) and LAST_NAME (= Master), the returned result is still NULL. The MySQL concat() function failed to return the proper results, because MIDDLE_INITIAL contains a NULL value.
Using simple straight forward SQL statements failed, due to a NULL field in MIDDLE_INITIAL. This is a visual example; something we can see in a result window. However, if I had a more complicated query and was using a NULL field in a JOIN, then the problem isn’t as interesting. The problem can even become frustrating.
Example: NOT NULL table redesign (following the data structure)
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CREATE TABLE security_users (
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id bigint(20) NOT NULL AUTO_INCREMENT,
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user_name varchar(30) NOT NULL,
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user_first_name varchar(20) NOT NULL,
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user_last_name varchar(20) NOT NULL,
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user_middle_initial varchar(1) NOT NULL DEFAULT ”,
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UNIQUE KEY user_name (user_name),
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PRIMARY KEY (id)
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) TYPE=InnoDB DEFAULT CHARSET=UTF8 AUTO_INCREMENT=1000;
In this table, MIDDLE_INITIAL has a value, even if the value is empty. An empty value is not the same as NULL and the results would return as I might expect them. The query in this post would execute properly and return the right results.
Working with MySQL Auto Incrementing Keys
If you’ve been working with Firebird, Oracle, or any number of other databases, the first thing you’ll want to understand is how to work with MySQL auto_increment keys. Anytime you work with keys that are auto incremented by the database engine, you will need a way to retrieve the key values for your insert statements. Relational database are built on joins and understanding how to assign your foreign keys is essential.
Using MySQL to manage your foreign key inserts you can use the LAST_INSERT_ID() function. This allows you to directly insert the value for your foreign keys without having to execute a query or some other mechanism. The LAST_INSERT_ID() MySQL function returns the value of the PRIMARY KEY previously inserted.
This works perfectly for simple designs where only a single foreign key exists and you want to link to the master table.
Example: Tables used
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CREATE TABLE web_template (
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id bigint(20) NOT NULL AUTO_INCREMENT,
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template_name varchar(30) NOT NULL,
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template_location varchar(100) NOT NULL,
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UNIQUE KEY template_name (template_name),
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PRIMARY KEY (id)
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) TYPE=InnoDB DEFAULT CHARSET=UTF8 AUTO_INCREMENT=1000;
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CREATE TABLE web_config (
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id bigint(20) NOT NULL AUTO_INCREMENT,
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config_template_id bigint(20) NOT NULL,
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PRIMARY KEY (id),
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FOREIGN KEY (config_template_id) REFERENCES web_template(id) ON DELETE CASCADE
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) TYPE=InnoDB DEFAULT CHARSET=UTF8 AUTO_INCREMENT=1000;
Example: Insert statements
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INSERT INTO web_template (template_name, template_location) VALUES (‘Default Template’, ‘/template/Default/’);
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INSERT INTO web_config (config_template_id) VALUES (LAST_INSERT_ID());
In PHP we have the mysql_insert_id() function, which allows us to retrieve the last key inserted. This function works pretty good, but it must be executed before you commit your transaction, otherwise you might get unexpected results. Additionally, it’s ideal to execute the statement directly after you submit your insert statement.
Using this function gives us more flexibility in key management in our applications, especially when working with tables that have multiple foreign keys.
Example: PHP statements
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<?php
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mysql_query("insert into web_template (template_name, template_location) values (‘Default Template’, ‘/template/Default/’");
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?>
Note: In a “data aware controls” environment, it’s not always easy to manage your auto incrementing keys (a lot of this is due to design, not just environment). In most cases where I have the decision making power I try to avoid data aware control development (especially on the web, now that Delphi for PHP is available). Read only grids are an exception, but most of the time you can design your applications to avoid “live data aware” entry/edit forms. It may seem like more work, but I believe in the end it’s cleaner and easier to debug.
How to Convert a Fireworks Image Design to HTML
In the last video in this mini site creation series I showed How to Design a Mini Site in Fireworks. In this video I show how to slice the image and export the image into HTML and then modify it into a very basic mini site.
There is nothing advanced in this tutorial, it’s just a very basic slice and export process with very minimal editing. This is to assist someone who has very little knowledge and experience with HTML. Basic understanding of using word processors and editing documents is all that’s required.
Please visit W3Schools to learn basic HTML programming.
I’ve created the two menu pages seen in the design image and created a link to the exported HTML mini site. You can view it here. I haven’t added anything to it that isn’t in the video. It is exactly how it was when I designed it in the video.
How to Design a Mini Site in Fireworks
In the last video series, I went through the process of How to Create eCovers (eBooks) and in this video I show how to design the mini site that compliments that eCover.
Mini sites are a pretty easy way to quickly create a website that is e-commerce ready. You can find tons of them on the internet in almost every genre imaginable. More commonly, the mini site serves the purpose of selling informational products, such as “How-to Make Money Online“. A somewhat horrible industry, due to the fact there is a lot stupid information available. I think most of that information is recycled garbage, modified by someone who promises riches, but has no idea what they are doing.
Nevertheless, the mini site is a powerful web site formula and not to be overlooked by someone with real talent and real knowledge. Understanding the formula and how to design and create the mini site is a valuable asset, as it can be used in many ways by both the entrepreneur and the freelancer.
The image below is the end result of this design video.
How to Create eCovers (FW+PS)(ebooks)
I use Adobe products for many things. I’m not a graphic artist, so I’ve never been able to master or even make good sense with Photoshop. However, Adobe Fireworks is easy to learn and a very powerful tool for me as a web developer.
In this video I use Adobe Photoshop and Adobe Fireworks to create an ebook cover.
To create modern day Web 2.0 style ebook covers, most everybody uses Action Scripts of some sort. In this video I am using Cover Action Pro scripts (a commercial product).
This video is about 25 minutes long and shows every step I took to create the eZine eCover in this post. My style might seem goofy to some Photoshop experts, but I’m a Fireworks user and all scripts that I am aware of at the moment are for Photoshop. So, I design the eCover in Fireworks and run the Photoshop scripts on the design.
