There is usually more than one way to write a given query, but not all ways are created equal. Some mathematically equivalent queries can have drastically different performance. This article examines one of the motivations for inventing LEFT OUTER join and including it in the SQL standard: improved performance through exclusion joins.
LEFT OUTER join syntax Read More →

Here’s a way to write join clauses so they are more compact, more readable, and less confusing.
Standard SQL:2003 defines a USING clause that can serve the same function as the ON clause in the familiar JOIN syntax. For example, the following join
select a.col1, b.col2
from a
inner join b on a.col3 = b.col3
May be Read More →

In this article I’ll show several ways to emulate a FULL OUTER join on a RDBMS that doesn’t support it, as is the case with even the most recent versions of MySQL. This useful query is surprisingly tricky to get right.
Introduction
A standard SQL FULL OUTER join is like a LEFT or RIGHT join, except that Read More →

Event delegation is an advanced technique for event-driven programming. The idea: instead of attaching one listener onto each element in a group, attach one listener onto an ancester shared by all the elements in that group. Then, when the listener is triggered, determine whether to act by looking at which element originally received the action.
The Read More →

Introduction to JSON
JSON (JavaScript Object Notation) is a lightweight data-interchange format (if you are new to JSON, you can read more about it on the JSON website). It is notably used by APIs all over the web and is a fast alternative to XML in Ajax requests. Prototype 1.5.1 finally features JSON encoding and parsing Read More →

Prototype enables you to deal with Ajax calls in a very easy and fun way that is also safe (cross-browser). Besides simple requests, this module also deals in a smart way with JavaScript code returned from a server and provides helper classes for polling.
Ajax functionality is contained in the global Ajax object. The transport for Read More →

Prototype's DOM extensions set it apart from other JavaScript libraries. Prototype adds many convenience methods to elements returned by the $() function: for instance, you can write $('comments').addClassName('active').show() to get the element with the ID 'comments', add a class name to it and show it (if it was previously hidden). The 'comments' element didn't have Read More →

In early versions of Prototype, the framework came with basic support for class creation: the Class.create() method. Until now the only feature of classes defined this way was that the constructor called a method called initialize automatically.
Prototype 1.6.0 now features a richer class system that's backward-compatible and adds some new features.
The cornerstone of class creation Read More →

Prototype takes the complexity out of client-side web programming. Built to solve real-world problems, it adds useful extensions to the browser scripting environment and provides elegant APIs around the clumsy interfaces of Ajax and the Document Object Model.
Getting started: Defining classes and inheritance • How Prototype extends the DOM • Introduction to Ajax • Using Read More →

Approximate joins
from the Artful Common Queries page

There are two main ways to reconcile payments against charges:

Open Item: match payments against individual charges, typically by carrying the charge number in the payments table
Statement: list and sum all charges and all payments, and show the difference as the outstanding balance.

The Open Item method needs a foolproof way Read More →

Parents without children
Given tables parent(id INT), child(id INT,parent_id INT), how do we find parents with no children? It's the All X for which there is no Y pattern, which can be written as an exclusion join...

SELECT parent.id
FROM parent
LEFT JOIN child ON parent.id = child.parent_id
WHERE child.parent_id IS NULL;

or with a NOT EXISTS subquery, which is logically equivalent to the exclusion join, but usually performs much slower:

SELECT parent.id AS ParentID
FROM parent
WHERE NOT EXISTS (
SELECT parent.id
FROM parent
JOIN child ON parent.ID = child.parent_id
);

Parties who Read More →

About the Abstract Factory
In the Abstract Factory Pattern, an abstract factory defines what objects the non-abstract or concrete factory will need to be able to create. The concrete factory must create the correct objects for it's context, insuring that all objects created by the concrete factory have been chosen to be able to work correctly Read More →