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Branch: master New pull request. Find File. Download ZIP. Sign in Sign up. Launching GitHub Desktop Go back. Launching Xcode Launching Visual Studio Fetching latest commit…. This would helpful to make a gud kick start. Since these type of technical stuffs would create interests within the beginners to learn more and perform more in this field of technology. For example, Supplier A changes their part number for Part x.
Now when you order Part X you need to quote their part number. By having an Identity column used for foreign keys, the new unique part number can be included in all purchase orders. The problem comes when that is the only key, not in the use of identity keys, one of the reasons being the one you stated about changing the natural key. I always set the primary key on every table that I create to be an integer, usually set by the identity property. Surrogate Keys I, too, initially misread your opinion of identities as surrogate keys.
I read the title of that section as:. I completely agree on the need for stable keys.
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Most of the time, Identities are much easier to implement and manage. Although purists would say that you are shirking your duty as a DBA to find a stable natural key. SP are a good practice, but they do have shortcomings: 1. NET SP 3. Column names I disagree on your assertion that column names should be end-user friendly.
Once you have the title right the rewrite should be easier. Use of identity columns in foreign key references Outstanding article. Most of your guidelines are indisputable. I was chief architect for Sybase back in the early s when we first added identity columns to SQL Server, so I have a bit of history with this topic. What happens if you use BCP to move data between databases?
Nuances Great article! Always use an intermediate table to BCP in prefferably with varchar-columns then process and check! You can use the natural key to do that. The conversation went something like this: P1: That data is stored in servletDatabase Me: Which server has the servlet database? P1: It is in the production database. Me: Thinking, a database in a database? P1: The data is in the table servletDatabase. Me: Of course, I should have realized that.
What happens when you have a server named playpen with a database named playpen and you have to rehost the playpen database, or when someone asks for a new server so they can get another database besides playpen. Finally can you imagine telling someone to look in the name column in name database, running on the name server? That is because natural keys mean something in the real world and therefore can change. As for having to BCP data around, that is when you switch to a GUID or equivalent surrogate key which is designed to be universally unique.
Saving Problem Thank you for this grear subject. I have a project with two tables…. Customers 2. It removes any new data I try to enter in any control as a textbox. If possible help me please. CLR proc is a good idea here. And do you include the length too? Too easy to query the metadata to waste time adding metadata to the name, in my opinion.
You are being ironically nieve. Too too too many times people just have an identity value, make it the primary key and they are done. So many forum posts start: I have duplicate key values…. I disagree here. You can choose to use natural keys for primary keys if you want, there is nothing wrong with it. I personally far identities, but there is noting wrong with it at all. In SQL Server, we can keep identity values when moving data around. And the PK being a clustered key helps joins out too. I would disagree here. I agree with you that I never like keys with values that can change.
That is a good idea, but I think that for the most part this is not a problem if you have named your objects to match what they are. Also, I usually speak of things in terms of what they are.
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If it did, the way you put it makes it non-ambiguous what you mean. Is this likely to happen like this? Probably not, since you will be naming your objects in a manner that makes sense, and it is unlikely that the database, table, and column would all have the same name..
Mistakes Your books are getting better, your writing is getting better, and your face is getting more robust. My last book had a magnificant crew working behind the scenes, which included the editor of this site. He was simply excellent to work with, which is why I came back here. Excellent Article I have been studying normalization for some time now and have been fighting the concept. A search for a clearer understanding is what brought me here. Now, I am a newbie and a lot of the stuff you are talking about above and beyond normalization is over my head but I have to compliment you on an a fantastic article.
I have gained a clearer understanding with regard to surrogate keys; something I never really understood. I was obviously taught incorrectly. It makes perfect sense.
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I love developing databases and hope to be technically where you are one day. Thank you for a great article and sharing your knowledge. I was wondering if you have written anything on design techniques. Microsoft is not my game but I could sure use your design knowledge. Nice column. Been in the position where people ahve done this and would not be pursuaded to see the light! I just do not agree with the 8th mistake. Brilliant arcticle Good argument on all rules and I generally agree on all. The domain value table rule might be overridden by dynamic database design, if that is needed.
I write web spiders for aggregating content Web 2. My tables can get very large the longer the spider runs. Thank you for info I am no wizz kid on databases, your article is great as it opens my eyes to some of the mistakes on database designs etc. Information like this is invaluable to us humble humans that are not too technical.
Thank you. Normalization I have set through two graduate level classes in Database and Object Oriented Development. In most instance, I was led to believe that with todays computing performance the idea of normalization is not as critical. But in fact you can not. Consider this frequent scenario. To investigate the impact of a proposed change, you need to review the documentation not just the code! Not surprisingly, your documentation external and internal contains the word Customer, say, 4, times.
How long will it take to read those? But if your table were named tblCustomer instead, the documentation might contain that word just 58 times, likely all of which are relevant. Thoughtful planning should minimize the expense of using documentation. Unless that Manager table contains historical data, this leaves you open to problems. But the use of the trigger sounds good.
Identity pk, not a good idea? One of the greatest problems when developing applications is that when the client wants to modify some field that are part of the primary key as a requirement you need to spend many hours to change this typical problem. Normalization is nothing more than forming the data in the way that it is natural to work with in SQL and eliminate redundancies that you have to maintain.
Performance-wise, you can expend energy keeping every redundancy straight, or you can expend energy calculating what you need when you need it. I also should make the point that while I completely believe in a normalized database structure, what is far more important is a normalized design. The problem comes in when you have structures that are not optimized to use in a relational database query processor and you have to do unnatural acts to get things to work, or you miss conditions that are super-important to your client….
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An interesting point. I would probably suggest a reasonable documentation pattern such as using [customer], or something like this, perhaps Customer table…. Good point. Code reviews are an essential part of the process so you have good coding practices, but the kind of testing I was referring to was making sure that the data is correct, which is more or less impractical in a code review.
I can only assume you are replying to another commenter, because I never design a table without an identity or guid, if forced primary key. One table… Does this issue illustrate the differences between application and database programming? For an application, performance is a direct function of code flexibility and efficiency because data is given to the application at the moment of use.
For databases, however, the data is already present so code that anticipates the users request gives higher performance. Good advice except for.. I agree with most of the points except… Store procedures are NOT a best practice. Most general purpose programming languages GPL are significantly more powerful than store procedures, and because of that you will create different architectures that can handle more requirements than you would with SP. Most GPL are OO and they have objects for encapsulation, inherritance and components for reuse, and offer much more expressiveness through dynamic binding.
Stored procedures are a left over from architecture modeling. There is some debate in my project on naming conventions. All the examples given to support NOT using stored procedures can be satisfied with non-store procedure solutions. Complex Busniness logic and Stored Procedures what is your take on this? Meaningless keys It is a vry strong argument that every column in a table should be meaningful.
But there is on important situation which I faced more than often, especially in material data: if you have to import data of limited quality and doubtful source XL etc. Another horrible real-world example: The newly designed 5-digit postal zip codes!!! After that things started to get fuzzy because that was all new to me except for the testing part. I fully anticipate that when they really start to use it the serious bugs will rear their nasty heads.
While planning our database improvement projects for this year, we realized that we probably need to create a master plan to detail what we want from our database. So, finally, my dilemma. How do I, as an engineer and a manager, communicate with our database team? Is there a format for creating a flowchart, or the like, that will help me to ogranize my ideas in a way that the implementors of our database will understand? Any advice is greatly appreciated. Thanks, Rob. Thank you! I am a newbie.
It was a great article to get me started. Normalization Ran across this article today. Obviously with any guidelines, one of the guidelines is that sometimes you have to deviate from them. I whole heatedly agree with the sentiment that, in general, if a user cannot differentiate between the rows, then a unique constraint is missing and that every table should have at least one unique constraint over fields other than the surrogate key.
It is very possible to have two John Smiths in our Person table that represent different humans. However, a user would differentiate one John Smith from another based on their addresses and phone numbers. ORM in some ways fits in with most of the best practices under the concept that every entity represents only one thing. The benefits of having a domain model mapped to classes with most languages are now the cornerstone of a lot of frameworks ex.
Ruby On Rails, Hibernate, etc. One thing that needs to be thought about now is when to use a stored procedure as opposed to retrieving data from an ORM framework. On the other hand, an ORM has built in capabilities to remap the data model to the new fields without needing to write sql. Sometimes it is a matter of adding a new property to a class. Views also have the advantage in that it can be mapped with ORM. Tough topic, but you nailed it! I have one more… Another thing I see that drives me crazy is lazy naming of columns, particularly in the case of subtypes that did not warrant their own table.
What I mean is when the database designer did not put enough thought into naming there attributes and just started naming columns as [entity]type, [entity]code or [entity]status. A classic example is UserStatus in a table called User. By lazy naming that attribute the door was left open for abuse of that column. It leads to derived values being added divorced, widowed , non-like values being added Married, Ineligible and conflicting values being added you can be married and Divorced at the same time.
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I can guarantee this will happen every time you see a column ending in code, type, status, or any generalization thereafter. It usually means the designer was just too lazy to give some thought into properly naming the column. In this case it should have been MaritalStatus, or even better there should be a separate table with marriage activities since a person can be married many times. Must Read article for beginers I read above article and immediately joined this forum.
This is must read for beginners like me. Thanks for sharing this with us! One table to hold all domain values : Great article, I partially agree in this one though. True, maintenance, queries and constraints have to be enforced by code, thus making the operation more challenging, but the end result can work beautifully. George Harrison must have been extremely old ….. It just goes to show that anyone can write anything on the internet these days and most will believe it. I wonder how much error or made up material without proper editorial exists? To a new user it would appear that way and of course they are not.
The truth I think is monotonically increasing integers minimizes page splits and help system performance. Using them as a surrogate primary key and by way of extension through the tools creates the typical clustered index. Re: Surrogate Keys, Genericizing Code The use of the identity key causes problems with a distributed database. Even Microsoft have started to warn people not to use it in such circumstances. A natural key works a lot better. The suggestion in your example that multiple PhoneNos or Addresses will uniquely identify a Person is not correct. They are multiples.
Two discrete John Smiths could have lived in the same Address. It will not help anyone uniquely identify a Person. All with the Person Identifier, in the Person table, not in some other table. Otherwise it is simply not a Relational table. Artificially making rows unique, by adding a surrogate key, does not make the row unique. They need to be minimised and used wisely.
In a Relational Database, the only valid circumstance for a Surrogate Key is when the natural relational PK is too wide to eg. A separate point. For those, Identity columns are fine. Because if so, then this is not true. You could conceivably have two babies born in the same hospital on the same day with the same name. You still need a truly unique identifier here SSN, etc. Thank you Mr. Bu this approach violates the integrity of my database : I cannot create a foreign relation between the the table of comments and the tables of objects posts, images etc.
Have you another solution to address this particular problem of inheritence without violating the integrity. What worked out for you? What are some of the techniques you use for testing? This article is helpful, thank you This article is helpful, thank you. It sounds like they are handy like function calls. I favor descriptive terms like tblProductID and I insist on using forms and other objects in such a way that no user, not even the DBA gets to see them anyway. The only access I give to a DBA as far as extra access is to add. I include a suggestion box for Db design wishes that can be accommodated when such things are a real priority.
No need for some dabbler to add things people want to the Db that ul;timately go unused anyway and only add to bloat. Rollin Shultz Allentown, Pa. Hi Louise, good article. And, most of the time, they should not even be exposed to users as they have no other meaning other than to tie one or several tables together. I cannot tell you the number of times I have seen RI problems in legacy systems that violated this rule. Thanks and have a great day! Hi sir John, I appreciate your answer. Please, I want to get deep understanding on these two points :.
How to use generated primary to tie tables in database? Please, Can you give some links that could help? After reading the article and then some of the comments and responses. Which is kind of odd, but can make sense I guess. Some times a thing is sitting right in front of you and one can fail to see it. A good read in as it was in Yet as I read, I still manage to commit one of the cardinal sins knowingly across the whole design — that of the primary key fallacy. However, well see below, happy to argue that with someone more knowledgeable! Why not just use schemas other than DBO, then keep the name as clean as possible?
SalesOrders, SAP. PurchaseOrders, CCU. Companies, CCU. It does need diagramming — I use Vertabelo to plan and brain storm this stuff out first as swapping schemas around may be awkward later down the line. Yes it does have the flaw that you can simply duplicate rows and I get this happening with inserts doing export projects. And support Table valued params on the code layer EF6. These look like a god send for complex business transactions done via web apps. I think it comes from the philosophy of database as dumb storage — nowadays one could use a NoSQL solution instead for that.
Yuk, hate them — think they are better off using a NoSQL solution instead, I believe there are all kinds of options that stop one breaking the data integrity notions of a sql database for generic tables. It took me a while to get through it but I did and understood most of it. My attached graphic describes my scenario. Thanks to all who chime in.
You want to use synthetic primary keys on every table. This provides an abstraction for each row and also for the natural key s which is what you want when joining tables. Try joining a table with a composite key; you will likely be inclined to concatenate the 2 keys when joining. You would also have to carry those 2 fields into every table you want to join from as a reference. This is eliminated with a synthetic or surrogate key. Also, joining using integers is the most performant wrt query execution.
This strategy provides the best of both: Guaranteed uniqueness of the natural key and a simplified and performant way to join tables using the surrogate key. Are you looking for a guarantee and a powerful spell that works without black magic or side infections visit shangosolutiontemple yahoo. Priest Okojie might be the answers to your problems. Free printable calendars that you can download, customize, and print. Superb information thanx for sharing. This would resulted in a clustered index which would be far more efficient when searching, in my opinion.
Still, I stand to be corrected, and therefore your comments on this would be greatly appreciated.
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The problem with this logic is that it is equating the clustered index with the primary key. The primary key is specifically a construct to prevent duplication, and provide the best value to access from other tables in foreign keys. The primary key may or may not be clustered. If CustomerId and PaymentId are the best for the clustered index based on testing, and not how it seems strictly by guesses, which we all start out with , then that makes perfect sense. However, what makes the best clustered key usually makes the best primary key because we often join on it, and even more so fetch more than a few columns from the table.
CustomerId, PaymentId 1 1 2 1 3 1. And so on. I assume that the cardinality of Payment to Customer is 1, so this is a problem that you have to be ready for when something goes awry. A non-clustered pk on PaymentId, and a clustered index on CustomerId, PaymentId gives you the performance you are looking for, with the protection you need. In such circumstances you mention, the clustered primary key would be used CustomerId, PaymentId and a unique constraints can be added to the PaymentId.
Compliant Database DevOps. Standardize team-based development Automate database deployments Monitor performance and availability Protect and preserve data. Development Operations IT Management. Home SQL. Consider the following example Customer table: Are there always 12 payments? Lack of documentation I hinted in the intro that, in some cases, I am writing for myself as much as you.
Subscribe for more articles Fortnightly newsletters help sharpen your skills and keep you ahead, with articles, ebooks and opinion to keep you informed. Simple Talk. Rate this article. Louis Davidson Louis has been in the IT industry for over 20 years as a corporate database developer and data architect. Follow Louis on. Since these type of technical stuffs would create interests within the beginners to learn more and perform more in this field of technology Amarjit Singh Kullar. Thanks for reading! Thanks for the article. I DO recommend stored procedures, but they are not always a best practice.
Replies 1. Replies To Mistakes: My last book had a magnificant crew working behind the scenes, which included the editor of this site. Thanks again, -Frank captonline at yahoo. It appears that you do not agree. Do we really need to be overly concerned with normalization? Goodness me Yes! Like exactly what an Artical is? To: Identity pk, not a good idea? Underscores in names? Hi, thank you so much for such an informative article!
Much thanks! To post a comment please sign in, or register if you are not already a member. I think that in the future better planning, user input, and testing will help me a lot. Views also have the advantage in that it can be mapped with ORM 3 Performance — when querying data involved multiple joins then stored procedures win hands down. Thanks for a nicely thought out article.
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