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Cross Joins

Sixth in a series of posts in response to Tim Ford's #EntryLevel Challenge.


Cross joins give all combinations of rows from two tables. They aren't normally useful, but they can be so in the right circumstances. One use for cross joins lies in generating large amounts of data for performance testing or similar purposes.

Exceptional SQL

Fifth in a series of posts in response to Tim Ford's #EntryLevel Challenge.


SQL implements a number of so-called union operators that under the right circumstances can make queries easy to write and intuitive to read and understand. One of these is the EXCEPT operator that "subtracts" one set of rows from another. 

Say for example that you're doing some work on data quality and want to investigate products that your firm has sold without ever having first purchased. What have you sold but never bought? You can answer that question easily by executing the following EXCEPT query:

The best Oracle Database idea since 1992: Putting the C into ACID (We need your vote)

Oracle Rdb (only available for the VMS platform) supports SQL-92 assertions (http://community.hpe.com/hpeb/attachments/hpeb/itrc-149/22979/1/15667.doc) so why not Oracle Database? Let’s put the “C” into “ACID.”(read more)

SQL Joinery

Fourth in a series of posts in response to Tim Ford's #EntryLevel Challenge.


SQL supports three types of join operation. Most developers learn the inner join first. But there are two other join operations you should know about. These are the outer join, and the full outer join. These additional join types allow you to write in essence could be termed as optional joins

Inner Joins

The so-called inner-join is the default. It's the happy path from a theory perspective, and it's the join type most SQL developers learn first. Use it to combine related rows from two or more tables. 

For example, perhaps you want to report on all the customers in the AdventureWorks database. You might begin working that business problem by writing the following query:

Video : Flashback Version Query

Today’s video gives a quick run through of flashback version query.

If you prefer to read articles, rather than watch videos, you might be interested in these.

Video : SQL/XML (SQLX) : Generating XML using SQL in Oracle

Another video fresh off the press.

If videos aren’t your thing, you can always read the article the video is based on.

The star of this video is Kevin Closson. Kevin’s a really nice guy and has a brain the size of a planet, but you know somewhere in the back of his mind he’s wondering what it would be like to hunt you down, kill you and mount your head above his fireplace. </p />
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ANSI Join Syntax in SQL Server

Another in a series of posts in response to Tim Ford's #EntryLevel Challenge.


Anyone new to SQL Server will sooner or later, and probably sooner, encounter exhortations to write joins in "ANSI join syntax". While the term is misleading and in fact incorrect, the practice of using the so-called "ANSI join syntax" contributes toward queries that are easier to understand and maintain. 

Clear Intentions

Following are two queries that produce the same result -- all possible combinations of product and subcategory names from the two tables listed in the FROM clause. (Such a result is termed a Cartesian product). Notice how I've written the joins in the respective FROM clauses.

The First and Last Word on NoSQL

Amazon had the first word on NoSQL but the creator of relational theory, Dr. E. F. Codd, gets the last word.(read more)

Video : XMLTABLE : Convert XML into Rows and Columns using SQL

Here’s an Easter present for everyone out there. </p />
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Video : The MERGE Statement

After a what seems like an eternity of being ill and having a dodgy throat, followed quickly by a couple of conferences, I’ve finally got back on the horse and recorded another video.

I was explaining a specific aspect of the MERGE statement to one of my colleagues and while I was doing it I was thinking, “Have I done a video on MERGE yet?” Now I have.

The cameo for this video is Cary Millsap. If you watch the out-takes at the end you will see the level of respect and trust I have garnered in the community. The words confused and suspicious spring to mind! :)