These concepts span data activities and it’s important that your team understand each other and where they, their tools and approaches need to support these features.
We’ll look at the generic and proprietary terms for these concepts, as well as where they fit in the database design process. We’ll also look at implementation options in SQL Server and other DBMSs.
Mar 15, 2016 // by Karen Lopez // Blog, Data Modeling, Database, Database Design, DLBlog, Speaking, SQL Server // No Comments
We’ll be chatting about all these questions and more on Thursday, 17 March at the Microsoft venue in Irving, Texas starting at 6PM.
Attendance is free, but you need to register at http://northtexas.sqlpass.org/ to help organizers plan for the event.
Don’t worry if you don’t know about SQL Server or don’t use it: this presentation will focus on some SQL Server specific features, but the discussion is completely portable to other DBMSs.
So many of us have learned database design approaches from working with one database or data technology. We may have used only one data modeling or development tool. That means our vocabularies around identifiers and keys tend to be product specific. Do you know the difference between a unique index and a unique key? What about the difference between RI, FK and AK? These concepts span data activities and it’s important that your team understand each other and where they, their tools and approaches need to support these features. We’ll look at the generic and proprietary terms for these concepts, as well as where they fit in the database design process. We’ll also look at implementation options in SQL Server and other DBMSs.
Tom LaRock (@sqlrockstar) posted today about clustered indexes on uniqueidentifiers. He has a great image there, which got me thinking about making my own….
Feb 16, 2012 // by Karen Lopez // Blog, Data, Data Modeling, Database, DLBlog, SQL Server // 5 Comments
I’ve highlighted the syntax that applies the IDENTITY to a column. SQL Server will know which column has the identity property (and you can only have one of these columns in the same table). Notice that there are only three options for an IDENTITY.
Notice that there is no TABLE or COLUMN referenced in that TSQL. You are just creating a SEQUENCE. SQL Server will have no idea what you are going to use it for or where it will be used. In fact, you could create a SEQUENCE and never use it. Notice there are several more options for a SEQUENCE.
SEQUENCEs are separate objects in a database and can be used to populate more than one column even across several tables. Because they aren’t bound to a table in any way, they can be used in ways that IDENTITY columns can’t be used. For instance:
One SEQUENCE can be used across more than one table. For instance, a Control Number or Document Number on several tables. I’ve seen this used in other DBMSs to generate document numbers across subtypes, say Purchase Orders, Shipping Notices, Return to Vendor Numbers, etc. There’s a requirement that they be unique across all types of documents. This could not be done with IDENTITY.
Using a SEQUENCE allows tables to have more than one auto-generated number in multiple columns. Think of Order Number and Cancellation Number, both on the Order table. You can’t do that with IDENTITY.
Since sequences are generated completely outside a table, you can chose to store the resulting value in a different format, say VARCHAR or CHAR. Or, heaven forbid, you might want to append data to it or do other kinds of evil to it before storing it.
Since sequences are generated completely outside a table, you can store the results in a NULLable column.
I think the confusion sets in because we tend to think of auto-generated number as useful only as surrogate keys. But we have real data needs for generating numbers other than just row identifiers, even if that’s the primary use for this. In fact, one could have a table with a PK that uses IDENTITY and an unlimited number of columns that use a SEQUENCE to set their values. Of course, SEQUENCEs can be used for surrogate primary keys, too. The existence of SEQUENCEs gives us another option over IDENTITY.
So SEQUENCE is a feature that just generates numbers based on some characteristics. A designer has many ways to use the number once it is generated and tables are not dependent on that method to get that number, nor do they even “know” about how that value was provided.
This separation of the COLUMN from how the data is populated is a feature of using SEQUENCEs. How one uses this separation depends on the technical and business requirements for the data.
This post is based on a post I previously blogged on 30 May 2008…but like most design approaches, it still holds true.
Everything is a trade off. You need to be able to explain, in both business and technical terms, the cost, benefits, and risks associated with every design decision.
If you can’t do that, then you aren’t doing design: you are copying design patterns from other designs and hoping for the best outcome, even if your current design has different requirements and risk tolerances.
I am often told that a database design must have surrogate keys on every table and that “right” way to implement surrogate keys is to use the Identity property in SQL Server (or the RowID in Oracle, or the Identity property in DB2). These sorts of features of modern DBMSs do vary from vendor to vendor, so the cost, benefit, and risk associated with each varies by version and by vendor. Most IT pros I speak with don’t realize that.
Many people I speak with assume, incorrectly, that Identity Property = Surrogate Key = Primary Key= Unique Index but this is not true. It is important for database designers to understand the differences between these concepts.
Nigel Rivett has written a great article over at Simple-talk.com about SQL Server’s identity property and some of the interesting “features” of this incrementing function:
Note: An identity column is not guaranteed to be unique nor consecutive. You should always place a unique index on an identity column if your system requires uniqueness.
I’m guessing that 6+ out of 10 of experienced SQL Server designers and developers are not clear on these two gotchas. Other DBMSs have technical issues as well. When I’m questioned on why I don’t just slap on an identity property, call it a PK an move on to the next change request, I usually start asking questions:
Will the application need to assume that the values are always sequential? What if the sequence is missing a few steps? Will that break the code?
Will the Identity column value be displayed anywhere outside the database, such as on a report or on a screen?
What are our plans for dealing with rows that exceed the maximum number of identity values (in some versions of DB2, identity values maxed out at 32k or so)?
Identity properties can be useful, but as in every design decision, there are uses that are appropriate and uses that are not — it all comes down to cost, benefit, and risk.
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The release goes on, “Respondents overwhelmingly agree that data not only helps them do their job better (97 percent) but enhances their credibility (87 percent). 74% agree their company would value them more if they improved their data literacy level. 82% said they would be willing to invest more time and energy into improving their data literacy skills. 93% of people that are reported as data literate say they are performing very well at work. Junior-level employees in the U.S. are among those least confident in completing data-oriented tasks, with only 21 percent classifying themselves as data literate. Middle managers (28 percent) in the U.S. are less likely to be data literate in comparison to C-suite executives (38 percent), despite using data more times per week in their positions.”
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The moral philosopher Cornel West (shaking hands with Obama), recently said if Barack Obama’s ascent to power was a morality play, he would be the voice of conscience. Rahm Emanuel, a cynical product of the Chicago political machine, would be Satan. Emanuel in the first scene of the play would dangle power, privilege, fame and money before Obama. West would warn Obama that the quality of a life is defined by its moral commitment, that his legacy will be determined by his willingness to defy the cruel assault by the corporate state and the financial elite against the poor and working men and women, and that justice must never be sacrificed on the altar of power. (click here for more on this Opinion piece by Chris Hedges)
David Arcus is a film composer based in Toronto Canada. He likes to write for orchestra, and guitar, and weird 80s synthesizers. Sometimes he'll just make bizarre sounds and build a score out of that. He likes the sound of analog tape even though it's expensive and impractical. He is also a producer. A little while back he was nominated for a Juno award for the album Flores, Tambores e Amores by Aline Morales, which he co-wrote and produced.
Proud to announce the release of the soundtrack for Knuckleball, a horror/thriller film I scored with Michelle Osis. This is truly one of the strangest and darkest scores I’ve worked on, and one of the most fun to write. We built most of the sounds from scratch by hitting, scraping and bowing a variety of metallic objects. To that we added live trombones, modular synths and a custom string instrument we built ourselves.
Consume (with Michelle Osis, 2017) short film, official selection Calgary International Film Festival
Great Great Great (2016) feature film, winner of Best Feature, Best Performance in a Feature, Best Screenplay, Canadian Film Fest
The Sisters Tolchinski (2016) short documentary, official selection Rhode Island International Film Festival
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Slifer Smith & Frampton has been fortunate to call Summit County home for over 12 years and over 50 years in Colorado. We look forward to helping you find your place in this special community. Click here for a printable community comparison snapshot.
This stock photo of California, San Francisco Bay, Golden Gate Bridge in the fog, Alamy Images number AE0T93, is available for licensing through Alamy Images for commercial and editorial uses including websites, books, magazines, brochures and advertising. Restrictions may apply for images which contain third party copyrighted material or sensitive subjects. Photos of artwork are for editorial use only.
This stock photograph id 5-740-72 of California, San Francisco Bay is © David Sanger Photography. All RIghts Reserved
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The Conservation District will supply poster board. Please call Connie at 270-685-1707 ext. 3 or email at connie.mills@ky.nacdnet.net to get them delivered to your school.
Each year the Kentucky Association of Conservation Districts awards three different scholarships in the amount of $1000.00. These state-wide scholarships are provided by the KACD Auxiliary. The scholarships are due to the District office by March 1st.
The Natural Resources Scholarship is awarded to any any student enrolled in college who has declared a major in the field of agriculture or conservation of natural resources.
The George Crafton Memorial Scholarship is awarded to any high school senior who is enrolled to attend college and intends to major in field of agriculture or related field.
The Betty Barrick Non-Traditional Student Scholarship is awarded to any student that is at least 25 years old and pursuing an undergraduate degree in agriculture or a related natural resource field.
If you've snooped around, you'll know that i'm originally from Minnesota. I grew up there, lived there til i was 22. After moving, i've grown even more appreciative of how beautiful it is. (in my opinion though, the snowy winter is not so tempting and i'm thankful to be away from that aspect.) I was searching through some photos from last September when i visited. I went up to one of my favorite spots in Red Wing. Thought of these pictures after a friend of mine, Danielle mentioned this place again to me. (i actually photographed her engagement photos!.. check them out here.) This spot is about 15 minutes from where i grew up, and is always a favorite place for a little adventure.
The Mississippi River, cross the bridge and you're in Wisconsin, and such a gorgeous view. What i love about this place is you can see the most of the city, and yet, you turn around walk and this is another view you'll get shortly.
It's always such a good adventure spot when i'm with Rachelle. If you haven't followed my posts long, you might have missed that Rachelle and her boyfriend recently visited me here in las vegas! what a great time to see her again! Rachelle let me photograph her and michael too! If you want to see those, click here! Super cute.
I constantly talk about Minnesota, and wanted to show just a glimpse into one of my favorite places. When i get to go back, i'll make sure to get photos of my other favorite places!
Not only is this a great place just for fun, but a beautiful area for photos, I've seen a few friends get some wedding photos up here too, so always consider a beautiful place like this!
Anyone have any guesses to another place i love to go? I'm thinking eventually i should have a giveaway, but one a little more fair... not based on my fave places.. so be ready for that! If there is a fun prize, does someone have one they'd like to see given away!?
The Tony Awards Show is an annual awards show recognizing the excellence achieved in live Broadway theater. Winners of the award receive a Tony Award, which is short for The Antoinetter Perry Award for Excellence in Theatre. The award is named after the co-founder of the American Theatre Wing, Antoinette Perry. Antoinette co-founded the award with Brock Pemberton.
The American Theatre Wing and The Broadway League host the awards show every year in New York City, New York. The awards are handed out for excellence in both Broadway productions and performances. The awards show also includes a couple discretionary non-competitive awards such as the Special Tony Award, the Tony Honors for Excellence in Theatre award, and the Isabelle Steveneson Award.
The first Tony Awards Show was held in 1947 and included 11 award categories. Currently there are 26 award categories that are part of either Performance Categories (actors/actresses) or Show & Technical Categories.
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