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Is it a common practice to use special naming conventions when you're denormalizing for performance?
For example, let's say you have a customer table with a date_of_birth column. You might then add an age_range column because sometimes it's too expensive to calculate that customer's age range on the fly. However, one could see this getting messy because it's not abundantly clear which values are authoritative and which ones are derived. So maybe you'd want to name that column denormalized_age_range or something.
Is it common to use a special naming convention for these columns? If so, are there established naming conventions for such a thing?
Edit: Here's another, more realistic example of when denormalization would give you a performance gain. This is from a real-life case. Let's say you're writing an app that keeps track of college courses at all the colleges in the US. You need to be able to show, for each degree, how many credits you graduate with if you choose that degree. A degree's credit count is actually ridiculously complicated to calculate and it takes a long time (more than one second per degree). If you have a report comparing 100 different degrees, it wouldn't be practical to calculate the credit count on the fly. What I did when I came across this problem was I added a credit_count column to our degree table and calculated each degree's credit count up front. This solved the performance problem.
I've seen column names use the word "derived" when they represent that kind of value. I haven't seen a generic style guide for other kinds of denormalization.
I should add that in every case I've seen, the derived value is always considered secondary to the data from which it is derived.
In some programming languages, eg Java, variable names with the _ prefix are used for private methods or variables. Private means it should not be modified/invoked by any methods outside the class.
I wonder if this convention can be borrowed in naming derived database columns.
In Postgres, column names can start with _, eg _average_product_price.
It can convey the meaning that you can read this column, but don't write it because it's derived.
I'm in the same situation right now, designing a database schema that can benefit from denormalisation of central values. For example, table partitioning requires the partition key to exist in the table. So even if the data can be retrieved by following some levels of foreign keys, I need the data right there in most tables.
Maybe the suffix "copy" could be used for this. Because after all, the data is just a copy of some other location where the primary data is stored. Since it's a word, it can work with all naming conventions, like .NET PascalCase which can be mapped to SQL snake_case, e. g. CompanyIdCopy and company_id_copy. And it's a short word so you don't have to write too much. And it's not an abbreviation so you don't have to spell it or ever wonder what it means. ;-)
I could also think of the suffix "cache" or "cached" but a cache is usually filled on demand and invalidated some time later, which is usually not the case with denormalised columns. That data should exist at all times and never be outdated or missing.
The word "derived" is just a bit longer than "copy". I know that one special DBMS, an expensive one, has a column name limit of 30 characters, so that could be an issue.
If all of the values required to derive the calculation are in the table already, then it is extremely unlikely that you will gain any meaningful (or even measurable) performance benefit by persisting these calculated values.
I realize this doesn't answer the question directly, but it would seem that the premise is faulty: if such conditions existed for the question to apply, then you don't need to denormalize it to begin with.
I've been reading a couple of questions/answers on StackOverflow trying to find the 'best', or should I say must accepted way, to name tables on a Database.
Most of the developers tend to name the tables depending on the language that requires the database (JAVA, .NET, PHP, etc). However I just feel this isn't right.
The way I've been naming tables till now is doing something like:
doctorsMain
doctorsProfiles
doctorsPatients
patientsMain
patientsProfiles
patientsAntecedents
The things I'm concerned are:
Legibility
Quick identifying of the module the table is from (doctors||patients)
Easy to understand, to prevent confusions.
I would like to read any opinions regarding naming conventions.
Thank you.
Being consistent is far more important than what particular scheme you use.
I typically use PascalCase and the entities are singular:
DoctorMain
DoctorProfile
DoctorPatient
It mimics the naming conventions for classes in my application keeping everything pretty neat, clean, consistent, and easy to understand for everybody.
Since the question is not specific to a particular platform or DB engine, I must say for maximum portability, you should always use lowercase table names.
/[a-z_][a-z0-9_]*/ is really the only pattern of names that seamlessly translates between different platforms. Lowercase alpha-numeric+underscore will always work consistently.
As mentioned elsewhere, relation (table) names should be singular: http://www.teamten.com/lawrence/programming/use-singular-nouns-for-database-table-names.html
Case insensitive nature of SQL supports Underscores_Scheme. Modern software however supports any kind of naming scheme. However sometimes some nasty bugs, errors or human factor can lead to UPPERCASINGEVERYTHING so that those, who selected both Pascal_Case and Underscore_Case scheme live with all their nerves in good place.
An aggregation of most of the above:
don't rely on case in the database
don't consider the case or separator part of the name - just the words
do use whatever separator or case is the standard for your language
Then you can easily translate (even automatically) names between environments.
But I'd add another consideration: you may find that there are other factors when you move from a class in your app to a table in your database: the database object has views, triggers, stored procs, indexes, constraints, etc - that also need names. So for example, you may find yourself only accessing tables via views that are typically just a simple "select * from foo". These may be identified as the table name with just a suffix of '_v' or you could put them in a different schema. The purpose for such a simple abstraction layer is that it can be expanded when necessary to allow changes in one environment to avoid impacting the other. This wouldn't break the above naming suggestions - just a few more things to account for.
I use underscores. I did an Oracle project some years ago, and it seemed that Oracle forced all my object names to upper case, which kind of blows any casing scheme. I am not really an Oracle guy, so maybe there was a way around this that I wasn't aware of, but it made me use underscores and I have never gone back.
I tend to agree with the people who say it depends on the conventions of language you're using (e.g. PascalCase for C# and snake_case for Ruby).
Never camelCase, though.
After reading a lot of other opinions I think it's very important to use the naming conventions of the language, consistency is more important than naming conventions only if you're (and will be) the only developer of the application. If you want readability (which is of huge importance) you better use the naming conventions for each language. In MySQL for example, I don't suggest using CamelCase since not all platforms are case sensitive. So here underscore goes better.
These are my five cents. I came to conclusion that if DBs from different vendors are used for one project there are two best ways:
Use underscores.
Use camel case with quotes.
The reason is that some database will convert all characters to uppercase and some to lowercase. So, if you have myTable it will become MYTABLE or mytable when you will work with DB.
Naming conventions exist within the scope of a language, and different languages have different naming conventions.
SQL is case-insensitive by default; so, snake_case is a widely used convention. SQL also supports delimited identifiers; so, mixed case in an option, like camelCase (Java, where fields == columns) or PascalCase (C#, where tables == classes and columns == fields). If your DB engine can't support the SQL standard, that's its problem. You can decide to live with that or choose another engine. (And why C# just had to be different is a point of aggravation for those of us who code in both.)
If you intend to ever only use one language in your services and applications, use the conventions of that language at all layers. Else, use the most widely used conventions of the language in the domain where that language is used.
C# approach
Singular/Plural
singular if your record in row contains just 1 value.
If it is array then go for plural. It would make perfect sense also when you foreach such element. E.g. your array column contains MostVisitedLocations: London, NewYork, Bratislava
then:
foreach(var mostVisitedLocation in MostVisitedLocations){
//go through each array element
}
Casing
PascalCase for table names and camelCase for columns made the best sense to me. But in my case in .NET 5 when I had json objects saved in dbs with json object names in camelCase, System.Text.Json wasnt able to deserialise it to object. Because your model has to be public and public properties are PascalCase. So mapping table columns(camelCase) and json object names(camelCase) to these properties can result in error(because mapping is case sensitive).
Btw with NeftonsoftJson this problem is not present.
So I ended app with:
Tables: App.Admin, App.Pricing, UserData.Account
Columns: Id, Price, IsOnline.
2 suggestions based on use cases:
Singular table names.
Although I used to believe in pluralizing table names once, I found in practise that there is little to no benefit to it other than the human mind to think in terms of tables as collections.
When singularising the table names, you can silently add -table to the singular table name in your head, and then it all makes sense again.
SELECT username FROM UserTable
Sounds more natural than
SELECT username FROM UsersTable
But post-fixing every table with is just a waste.
The actual practical argumentation for singularising table names:
What is the plural of person: persons or people?
This is still ok.
But how do you like a table with postfix -status? Statuses?
That sucks, sorry.
It is easy to inadvertently make a human mistake by singularizing the status table, but pluralizing the other tables.
PascalCasing + Underscore convention.
Given table User, Role and a many-to-many table User_Role.
Considering underscore cased user_role is dubious when all table names are using underscore per default.
Is user_role a table that contains user roles? In this case it is not, it is a join table.
When deciding on table name conventions I think it is useful to let go of personal preference and take into account the real practical considerations of real life problems in order to minimize dubious situations to occur.
As the many answers and opinions have indicated, whatever your personal opinion is, different people think differently, and you will not be the only person working on the database despite being the one who sets it up (unless you do, in which case you're only helping yourself).
Therefore it is useful to have practical argumentation (practical in the sense of, does it help my future co-workers to avoid dubious situations) when your past decision is being questioned.
Unfortunately there is no "best" answer to this question. As #David stated consistency is far more important than the naming convention.
there's wide variability on how to separate words, so there you'll have to pick whatever you like better; but at the same time, it seems there's near consensus that the table name should be singular.
We are going to develop a new system over a legacy database(using .NET C#).There are approximately 500 tables. We have choosen to use an ORM tool for our data access layer. The problem is with namig convention for the entities.
The tables in the database have names like TB_CUST - table with customer data, or TP_COMP_CARS - company cars. The first letter of prefix defines the modul and the second letter defines its relations to other tables.
I would like to name the entities more meaningful. Like TB_CUST just Customer or CustomerEntity. Of course there would be a comment pointing to its table name.
But the DBA and programer in one person, dont want names like this. He wants to have the entities names exactly the same to the table names. He is saying that he would have to remember two names and it would be difficult and messy. I have to say his not really familiar with the principles of OOP.
But in case of an entity name like TP_COMP_CARS there should be methods names like Get TP_COMP_CARS or SaveTP_COMP_CARS..I think this is unreadable and ugly.
So please tell me your opinion. Who is right and why.
Thank you in advance
The whole idea of ORM tools, is to avoid the need of remembering database objects.
We usually create a database class with all the table and column names, so no one needs to remember anything, and the ORM should map database "names" to normal entities.
Although it is subjective, in my opinion you are right and he is wrong....
Who is going to work mostly with the new code? That person should decide the naming convention IMHO.
Personally of course I would go for your solution because as has already been mentioned, if you use ORM you don't need to hit the DB directly often.
As a compromise you could use names like TB_CUST where act directly with the database but then use names like Customer for your Data Transfer Objects. Writing good code involves creating an abstraction of any datasources you might be working with. Have GetTB_CUST() throughout your code is a little like having GetTB_CUSTFromThatSQLDatabaseWeHave() dotted around the place.
I personally hate table names like that, but it's a legacy system and I'm sure the DBA doesn't feel like renaming the tables. Renaming the tables could be an option. You would just have to create views representing the old table names so that your legacy system keeps running while you develop your new system. If this is not an option you can use the ORM to map table names to entity names. Or you can abstract your ORM away in a data access layer and define nice entity names in your domain model, having your DAL do the name conversion.
The naming conventions used in two different domains simply don't align. Java, for example, hasa very well defined rules/conventions for Class names and field names, where capitalisation is significant. In general, your application may be ported to a completely different Database with a different naming standard, it's not reasonable to demand alignment of names in Business Logic with names in Database. Consider a slightly more complex mapping, one Entity may not correspond to one Table.
And, really, come on ...
Customer == TB_CUST
That is just not so hard! I'm with you, makes the names meaningful in the code and map in the ORM. The learning for the DBA/Programmer should not be that painful, my guess is that it's one of those things that feels much worse in the anticipation than the reality.
If there are 500 tables in the database - you've already got a challenge keeping those names straight. Hopefully, you've got metadata and some graphical models that describe them more meaningfully.
When you create the next 500 ORM objects - you'll have another challenge. Even if you give them meaningful names it's still too many to really hope that all will be obvious. So, now you've got 2 problems.
If there's no way to link those two sets of 500 tables together - then you've got 3 problems. Think about debugging performance of queries in the ORM, and going to the DBA with names that he doesn't recognize. Think about your carefully crafted names - that then must be ignored when you create reports that hit the database directly.
So, I'd try very hard to use the database names in the ORM. But I would tweak a few things:
if a name is too cryptic to understand - I'd work with the DBA to improve its name. An easy way to transition to better names is through views. Ideally you get rid of the original confusing name eventually tho.
changing from underscores to camelcase, etc shouldn't be considered a change to the name - it's just a change to the separator. So, use the appropriate name for your language.
the database prefixes can probably be dropped - they're actually just attributes of the table name that have been "denormalized" and grafted onto the name. They may be necessary to avoid duplication if they indicate a subsection of the model, but in general may be be as important.
"I have to say his not really familiar with the principles of OOP.
But in case of an entity name like TP_COMP_CARS there should be methods names like Get TP_COMP_CARS or SaveTP_COMP_CARS..I think this is unreadable and ugly.
So please tell me your opinion. Who is right and why."
Which names are given to the things your IT systems manages has absolutely nothing to do with "the principles of OOP".
The same holds for which names are given to "standard" "getter and setter" methods : those are just agreements and conventions, not "principles of OOP".
The issue is a certain kind of "ergonomics" (and thus also the self-documenting value) of the code.
It is true that getTP_COMP_CARS looks ugly (though not, as you claim, "unreadable"). It is also true that if you start adhering to "more modern" naming conventions, then there will have to be someone somewhere who will have to maintain a mapping between the names that are synonymous. (And it is untrue that names such as TP_COMP_CARS are less self-documenting than full "natural-language-words" names : usually such names are constructed from a VERY SMALL set of mnemonic words that are used over and over again with the same meaning, making it more than easy enough for anyone to remember them.)
There is no right and wrong about this. Names like that were the usual convention in the days before the ones we live in now. At least, those names usually had the benefit of being case-insensitive, as opposed to the braindead (because case-sensitive) naming rules that are imposed upon us by so-called "more modern" systems.
Twenty years from now, people will call the naming conventions we use these days "braindead" too.
You usually normalize a database to avoid data redundancy. It's easy to see in a table full of names that there is plenty of redundancy. If your goal is to create a catalog of the names of every person on the planet (good luck), I can see how normalizing names could be beneficial. But in the context of the average business database is it overkill?
(Of course I know you could take anything to an extreme... say if you normalized down to syllables... or even adjacent character pairs. I can't see a benefit in going that far)
Update:
One possible justification for this is a random name generator. That's all I could come up with off the top of my head.
Yes, it's an overkill.
People don't change their names from Bill to Joe all at once.
Database normalization usually refers to normalizing the field, not its content. In other words, you would normalize that there only be one first name field in the database. That is generally worthwhile. However the data content should not be normalized, since it is individual to that person - you are not picking from a list, and you are not changing a list in one place to affect everybody - that would be a bug, not a feature.
How do you normalize a name? Not all names have the same structure. Not all countries or cultures use the same rules for names. A first name is not necessarily just a first name. People have variable numbers of names. Some countries don't have the simple pair of firstname/lastname. What if my first name just so happens to be your last name, should they be considered the same in your database? If not, then you get into the problem that last name might mean different things in different countries. In most countries I know of, it is a family name. Your last name is the same as at least one of your parents' last name. On Iceland, it is your father's first name, followed by "son" or "daughter". So the same last name will mean completely different things depending on whether you encounter it in Iceland and the US.
In some cultures it is common when getting married, for the woman to take her husband's last name. In other cultures, that's completely optional, or might even work the opposite way.
How can you normalize this? What information would it gain you? If you find someone in your database who has "Smith" as the last word making up their name, what does that tell you? It might not be their family name. It might only be part of the family name. It might be an honorary in some language, but which according to their culture, should be considered part of the name.
You can only normalize data if it follows a common structure.
If you had a need to perform queries based on diminutive names I could see a need for normalizing the names. e.g. a search for "Betty" may need to return results for "Betty", "Beth", and "Elizabeth"
Yes, definitely overkill. What's a few dozen bytes betewen friends?
Maybe if you work in the Census office it might make sense. Otherwise, see every other answer :)
I would say yes, it is going too far in 95%+ of the cases.
Yes. I cannot think of an instance where the benefits outweigh the problems and query complications.
No, but you might want to normalise to a canonical record for a customer (so you don't get 5 different entries for 'Bloggs & Co.' in your database. This is a data cleansing issue that often bites on MIS projects.
You often don't go over fourth form normalization in a database. Therefore seventh form normalization is quite a bit overboard. The only place this might even be a remotely plausible idea is in some kind of massive data warehouse.
Generally yes. Normalizing to that level would be going to far. Depending on the queries (such as phone books where searches by last name are common) it might be worthwhile. I expect that to be rare.
I generally haven't seen a need to normalize the name, mainly because that adds a performance hit on the join that will always be called, and doesn't give any benefit.
If you have so many similar names, and have a storage problem then it may be worth it, but there will be a performance hit that would need to be considered.
I would say it is absolutely overkill. In most applications, you display folks' names so often, every query involved with that is going to look that much more complex and harder to read.
Yes, it is. It is commonly recognized that just applying all of the Rules of Normalization can cause you to go way too far and end up with an overnormalized database. For example, it would be possible to normalize every instance of every character to a reference to a character enumeration table. It's easy to see that that's ridiculous.
Normalization needs to be performed at a level that is appropriate for your problem domain. Overnormalization is as much a problem as undernormalization (although, of course, for different reasons).
There might be a case where being able to link married/maiden names would be useful.
Recently had a case where I had to rename thousands of emails in exchange because somebody got divorced and didn't want any emails listing her as married_name#company.com
No need to normalize to that level unless the names make up a composite primary key and you have data that is dependant on one of the names (e.g. anyone with the surname Plummer knows nothing about databases). In which case, by not normalizing, you would violate second normal form.
I agree with the general response, you wouldn't do that.
One thing comes to mind though, compression. If you had a billion people and you found that 60% of first names were pulled from 5 very common names, you could use some tricky bit manipulation to reduce the size very significantly. It would also require very customized database software.
But this isn't for the purpose of normalization, just compression.
You should normalize it out if you need to avoid the delete anomaly that comes with not breaking it out. That is, if you ever need to answer the question, has my database ever had a person named "Joejimbobjake" in it, you need to avoid the anomaly. Soft deletes is probably a much better way than having a comprehensive first name table (for example), but you get my point.
In addition to all the points everyone else has made, consider that if you were implementing a data entry operation (for example), and were to insert a new contact, you would have to search your first name and last name tables to locate the correct Id's and then use those values. But then this is further complicated by the occasion when the name is not on the FN and/or LN tables, then you have to insert the new first/last name and use the new id(s).
And if you think that you have a comprehensive list of names, think again. I work with a list of over 200k unique first names and I'd guess it represents 99.9% of the US population. But that .1% = a lot of people. And don't forget the foreign names and misspellings...
I've got a question concerning fields in databases which are measures that might be displayed in different units but are stored only in one, such as "height", for example.
Where should the "pattern unit" be stated?. Of course, in the documentation, etc... But we all know nobody reads the documentation and that self-documented things are preferable.
From a practical point of view, what do you think of coding it in the database field (such as height_cm for example)?.
I find this weird at a first look, but I find it practical to avoid any mistakes when different people deal with the database directly and the "pattern unit" will never change.
What do you think?
What's weird about height_cm? Looks good to me.
Sometimes you see measures and units in two separate fields, which is much more painful.
As long as you know the units aren't going to change, I think height_cm is a good way to deal with it.
Most databases support comments on columns. For example in Postgres you could set a comment like this:
COMMENT ON COLUMN my_table.my_column IS 'cm';
Storing the unit name this way means your database is self-documenting.
I would also strongly recommend using standard scientific units (i.e. the metric system).
Be wary about measures that may change like currencies. In many cases it is not practical rename database field when it's measure changes.
It is rather silly to have a field called amount_mk which used to contain money amount in marks but currently actually contains money amount in euros.
I agree, nothing wrong with adding the unit to the field name.
The only thing I'd say is to make the naming convention consistent across your database - i.e. avoid situations where you have both height_cm and mm_width present in the same database!