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I am using a SQLAlchemy database to hold data for a flask application. I would like one column in my database to represent a category (e.g. the possible categories may be A, B or C).
I have seen in documentation that this can be achieved by a simple relationship which relates two tables. One table to hold some live data (inclusive of a category ID and a category) and another table to relate a category id to the associated category. http://flask-sqlalchemy.pocoo.org/2.3/quickstart/#simple-relationships
Would this method be considered good practice for including some kind of "category" column in my database? Or is there a simpler/better way. In this case my aim is to prioritise simplicity while maintaining good practice (don't really need best practice if it entails too much complexity).
Additionally, if my category names will never change, is it bad practice to use a constant list of category names to compare input data with in order to validate it? If so, why?
This is more of an SQL question and it isn't related to Python at all.
Anyways, it is actually better to use a reference table as you first suggested.
In this case, a Category table with one-to-many relationship. This allows you to change category name, and enrich Category with more details (like description) that might become useful in the future.
The other way, using constant list, is considered a bad practice - especially using Enums. You can read more about it in this article: 8 Reasons Why MySQL's ENUM Data Type Is Evil
You can read more about this dilemma here.
Hope it helps.
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I have some ideas, some that I have accumulated over time, but I really want to know what makes things go smoothly for you when modeling database:
Table name matches Primary Key name and description key
Schemas are by functional area
Avoid composite primary keys where possible (use unique constraints)
Camel Case table names and field names
Do not prefix tables with tbl_, or procs with SP_ (no hungarian notation)
OLTP databases should be atleast in BCNF / 4NF
Name similarly targetted stored procs with the same prefix, for instance if you've got 3 stored procedures for Person. That way everything for person is grouped in one place and you can find them easily without having to look through all your procs to find them.
PersonUpdate
PersonDelete
PersonCreate
Do similar things for tables when you have groups of tables with related data. For instance:
InvoiceHeaders
InvoiceLines
InvoiceLineDetails
If you have the option of schemas within your database, use them. It's much nicer to see:
Invoice.Header
Invoice.Line.Items
Invoice.Line.Item.Details
Person.Update
Person.Delete
Person.Create
Don't use triggers unless there's no other reasonable approach to achieve that goal.
Give field names a meaningful prefix so you can tell what table they come from without someone needing to explain. That way when you see a field name referenced, you can easily tell which table it's from.
Use consistent data types for fields containing similar data, i.e. don't store phone number as numeric in one table and varchar in another. In fact, don't store it as numeric, if I come across a negative phone number I'll be mad.
Don't use spaces or other obscure characters in table/field names. They should be entirely alphanumeric - or if I had my druthers, entirely alphabetic with the exception of the underscore. I'm currently working on an inherited system where table and field names contain spaces, question marks and exclamation marks. Makes me want to kill the designer on a daily basis!
Don't use syntax keywords as object names it'll cause headaches trying to retrieve data from them. I hate having to wrap object names as [index] that's two needless chars I didn't need to type damn you!
One thing I haven't seen mentioned yet:
Never use database keywords as object names. You do not want to have to qualify them every time you use them
If you misspell something when you create it, fix it as soon as you notice it. Don't spend years having to remember that in this table UserName is really Usernmae. It's a whole lot easier to fix when there isn't much code written against it.
Never use implied joins (the comma syntax), always specify the joins.
Putting everybody's input together into one list.
Naming Standards
Schemas are named by functional area (Products, Orders, Shipping)
No Hungarian Notation: No type names in object names (no strFirstName)
Do not use registered keywords for object names
No spaces or any special characters in object names (Alphanumber + Underscore are the only things allowed)
Name objects in a natural way (FirstName instead of NameFirst)
Table name should match Primary Key Name and Description field (SalesType – SalesTypeId, SalesTypeDescription)
Do not prefix with tbl_ or sp_
Name code by object name (CustomerSearch, CustomerGetBalance)
CamelCase database object names
Column names should be singular
Table names may be plural
Give business names to all constraints (MustEnterFirstName)
Data Types
Use same variable type across tables (Zip code – numeric in one table and varchar in another is not a good idea)
Use nNVarChar for customer information (name, address(es)) etc. you never know when you may go multinational
In code
Keywords always in UPPERCASE
Never use implied joins (Comma syntax) - always use explicit INNER JOIN / OUTER JOIN
One JOIN per line
One WHERE clause per line
No loops – replace with set based logic
Use short forms of table names for aliases rather than A, B, C
Avoid triggers unless there is no recourse
Avoid cursors like the plague (read http://www.sqlservercentral.com/articles/T-SQL/66097/)
Documentation
Create database diagrams
Create a data dictionary
Normalization and Referential Integrity
Use single column primary keys as much as possible. Use unique constraints where required.
Referential integrity will be always enforced
Avoid ON DELETE CASCADE
OLTP must be at least 4NF
Evaluate every one-to-many relationship as a potential many-to-many relationship
Non user generated Primary Keys
Build Insert based models instead of update based
PK to FK must be same name (Employee.EmployeeId is the same field as EmployeeSalary.EmployeeId)
Except when there is a double join (Person.PersonId joins to PersonRelation.PersonId_Parent and PersonRelation.PersonId_Child)
Maintenance : run periodic scripts to find
Schema without table
Orphaned records
Tables without primary keys
Tables without indexes
Non-deterministic UDF
Backup, Backup, Backup
Be good
Be Consistent
Fix errors now
Read Joe Celko's SQL Programming Style (ISBN 978-0120887972)
My standards for Oracle are:
Keywords are always in UPPERCASE;
Database object names are always in lowercase;
Underscores will replace spaces (ie there won't be any camel case conventions that are common on, say, SQL Server);
Primary keys will pretty much always be named 'id';
Referential integrity will be enforced;
Integer values (including table ids) will generally always be NUMBER(19,0). The reason for this is that this will fit in a 64-bit signed integer thus allowing the Java long type to be used instead of the more awkward BigInteger;
Despite the misnomer of appending "_number" to some column names, the type of such columns will be VARCHAR2 not a number type. Number types are reserved for primary keys and columns you do arithmetic on;
I always use a technical primary keys; and
Each table will have its own sequence for key generation. The name of that sequence will be _seq.
With SQL Server, the only modification is to use camel case for database object names (ie PartyName instead of party_name).
Queries will tend to be written multi-line with one clause or condition per line:
SELECT field1, field2, field2
FROM tablename t1
JOIN tablename2 t2 ON t1.id = t2.tablename_id
WHERE t1.field1 = 'blah'
AND t2.field2 = 'foo'
If the SELECT clause is sufficiently long I'll split it out one field per line.
Name all constraints
don't forget to back up your databases on a regular basis.
Don't use type names in the field names. The older guys will remember the old MS standard of lpszFieldName and the stupidity that ensued.
Use descriptive field names That follow normal language conventions. For example "FirstName" instead of "NameFirst"
Each word in the field name is capitalized
No underscores
Do not use normal keywords such as "Index"
Do not prefix ANYTHING with the object type. For example we do NOT use tblCustomers or spCustomersGet. These don't allow for good sorting and provide zero value.
Use schemas to define separate areas of the database. Such as sales.Customers and hr.Employees. This will get rid of most of the prefixes people use.
Loops of any kind should be viewed with suspicion. There's usually a better set based way.
Use views for complicated joins.
Avoid complicated joins when possible. It may be more astheticaly pleasing to have a CustomerPhoneNumbers table; but honestly, how many phone numbers do we really need to store? Just add the fields to the Customers table. Your DB queries will be faster and it's much easier to understand.
If one table calls a field "EmployeeId" then EVERY SINGLE TABLE that references it should use that name. It doesn't need to be called CustomerServiceRepId just because it's in an extension table.
Almost all tables have the "s" ending. For example: Customers, Orders, etc. After all the table holds many records...
Evaluate your queries, indexes and foreign key relationships with an analysis tool. Even those that may be generated for you. You might be surprised.
Linking tables which support many to many relationships have both linked tables in the name. For example, SchoolsGrades. It's very easy to tell by the table name what it does.
Be CONSISTENT. If you start down one path with your conventions, don't change horses halfway unless you are willing to refactor all of the previous work. This should put the brakes on any "wouldn't it be great if.." ideas that end up causing confusion and vast amounts of rework.
Think before you type. Do you really need that table, field, sproc, or view? Are you sure it isn't covered somewhere else? Get concensus before adding it. And if for some reason you have to take it out, talk to your team first. I've been at places where the DBA's make daily breaking changes without regard for the devs. This isn't fun.
If a database is for a particular application, have a version table so that the database releases can be checked against the code releases (amongst other reasons).
I always try not to use the type in the field name - "sFirstName", "sLastName", or "iEmployeeID". While they match at first, if something changes, they'll be out of sync, and it's a huge headache to change those names later, since you have to change the dependant objects as well.
Intellisense and the GUI tools make it trivial to find out what type a column is, so I don't feel this is necessary.
The WITH clause really helps break queries down into manageable parts.
It also really helps for efficiency on the execution plans of the queries.
Ensure that every varchar/nvarchar choice is appropriate.
Ensure that every NULLable column choice is appropriate - avoid NULLable columns where possible - allowing NULL should be the justifiable position.
Regardless of any other rules you might use from the suggestions here, I would create a stored procedure in the database that can be run on a regular basis to determine system health for any rules or standards you do have (some of this is a little SQL-Server specific):
Look for orphaned records in any cases where the DBMS system's referential integrity cannot be used for some reason (in my system I have a table of processes and a table of tests - so my system_health SP looks for processes without tests, since I only have a one-way FK relationship)
Look for empty schemas
Look for tables without primary keys
Look for tables without any indexes
Look for database objects without documentation (we use SQL Server Extended properties to put the documentation in the database - this documentation can be as granular as the column).
Look for system-specific issues - tables which need to be archived, exceptions which are not part of normal monthly or daily processing, certain common column names with or without defaults (CreateDate, say).
Look for non-deterministic UDFs
Look for TODO comments to ensure that code in the DB does not somehow have untested or pre-release code.
All this can be automated to give you an overall picture of system health.
Everyone writes SQL queries (views, stored procedures, etc) in the same basic format. It really helps development/maintenance efforts down the road.
Consistent naming standards. Having everyone on the same page, using the same format (whether it be Camel Case, specific prefixes, etc..) helps in being able to maintain a system accurately.
A few likes and dislikes.
My opinion is prefixes are horrible in every aspect. I currently work on a system where the tables are prefixed, and the columns within the tables are prefixed with 2 letter table name acronyms, I waste at least 30 mins each day working on this database because the acronym isn't logical. If you want to denote something with a prefix use a schema owner instead.
Using NVarchar from the start of a project if there is even a slight hint that down the line the text data will need to support multi lingual chars. Upgrading large databases because of lack of forward planning and thinking is a pain and wastes time.
Splitting each condition within a where clause onto a new line for readability (in and not in statements wrapped in brackets and tabbed in.) I think this is the important standard for me.
I worked at one company where a standard was that comma's must always be placed at the start of a line when performing parameter or variable declarations. This apparently made it more readable however I found it a complete nightmare.
In addition to normalization to 3NF or BCNF (more about that in this question), I have found the following to be useful:
Name tables as plural nouns
Name columns as sigular
So a "People" table has a "PersonID" column.
There is nothing wrong with composite keys, so long as the rules of 3NF or BCNF still hold. In many cases (such as the "many-to-many" case) this is entirely desirable.
Avoid repeating the table name in the column names. peoplePersonID is better written as table.column anyway, and much more readable and therefore self-documenting. People.PersonID is better, to me at least.
ON DELETE CASCADE should be used very carefully.
Remember that NULL means one of two things: Either it's unknown or it's not applicable.
Remember also that NULLs have interesting affects on joins, so practice your LEFT, RIGHT, and FULL outer joins.
Some others (albeit small) comments to throw against the wall...
SQL Server database schemas can be useful for both organizing tables and stored procedures as well as controlling security.
Every transactional table should always track both who and when created the record as well as updated the record in separate columns. I've seen implementation that simply used "update date" which can lead to auditing challenges in the future.
Use GUID's for row identifiers for all rows for projects with offline/synchronization requirements.
Good database design and normalization.
Tables are named in the singular, lowercase, no underscores, no prefix
Fields also lowercase, no underscores, no prefix
Stored procedures prefixed with "st_" (sorts nicely)
Views that are treated like tables have no prefix
Views created for special reports, etc. have a "v" prefix
Indexed views created for performance have an "ixv" prefix
All indexes have purposeful names (no auto-naming)
Strongly prefer uniqueidentifier (with sequential increment) over int IDENTITY for surrogate keys
Don't artificially limit VARCHAR/NVARCHAR fields to 100 or 255. Give them room to breath. This isn't the 1980s, fields are not stored padded to their max length.
3NF minimum standard
Prefer joining tables to column-level foreign keys: many 1:m assumptions are challenged as a system grows over time.
Always use surrogate keys, not natural keys, as the primary key. All assumptions about "natural" keys (SSNs, usernames, phone numbers, internal codes, etc.) will eventually be challenged.
Tabular formatted SQL.
select a.field1, b.field2
from any_table a
inner join blah b on b.a_id = a.a_id
inner join yet_another y on y.longer_key = b.b_id
where a.field_3 > 7
and b.long_field_name < 2;
Part of this is to use uniformly long alias names (in the example, here, a, b, and y are all length 1).
With this kind of formatting, I can more quickly answer common questions like, "what table is aliased by 'a'?" and "which fields join table T into the query?" The structure doesn't take long to apply or to update, and I find that it saves a lot of time. We spend more time reading code than writing it.
Document everything; wiki type documentation is easy to setup and the software is free.
Make sure you understand the interface first and design the database second. Most of the time its a lot better to know how the data you are going to use needs to work and then engineer the database. Most bad DB design happens as things evolve not upfront.
Then define the database standard and version you are going to work to. Define standards for the code elements (views, functions etc), database naming; naming conventions for columns, tables; type conventions for columns; coding templates.
Spend time considering how you define types having standard database types for fields or bespoke types are a good thing to sort out upfront.
As part of your documentation include a list of don'ts as well as dos for the application which include your prefered hated functionality cursors, triggers.
Review it regularly.
13- Evaluate your queries
Thats true. Sometimes you don't get what you wanted.
For me, it's always useful to name the tables and fields with their exact content and (for us) in clear spanish and using Upper Camel Case, with no whitespaces:
User Name: NombreUsuario
First Last Name: ApellidoPaterno
Second Last Name: ApellidoMaterno
etc etc
Taking "database" to mean "SQL product", my answer is, "Too many to mention. You could write a whole book on the subject." Happily, someone has.
We use Joe Celko's SQL Programming Style (ISBN 978-0120887972): "this book is a collection of heuristics and rules, tips, and tricks that will help you improve SQL programming style and proficiency, and for formatting and writing portable, readable, maintainable SQL code."
Advantages of this approach is include:
the guy knows more about this kind of thing than me (is there another book on SQL heuristics?!);
the work has already been done e.g. I can give the book to someone on the team to read and refer to;
if someone doesn't like my coding style I can blame someone else;
I recently got a load of rep on SO by recommending another Celko book :)
In practice we do deviate from the prescriptions of The Book but surprisingly rarely.
In MS-SQL, I've always had objects owned by dbo., and I prefix calls to those objects with dbo.
Too many times I've seen our devs wonder why they can't call their objects that they inadvertainly owned.
Avoid silly abbreviation conventions, such as comprehensive dictionaries of abbreviations that actively encourage monstrosities like EMP_ID_CONV_FCTR_WTF_LOL_WAK_A_WAK_HU_HU. This rule is inspired a real set of guidelines I've seen before.
MVP Aaron Bertrand's
"My stored procedure "best practices" checklist"
Table name matches Primary Key name and description key
I have just recently, after years of agreeing with this, jumped ship, and now have an "ID" column on every table.
Yes I know, when linking tables it's abiguous! But so is linking ProductID to ProductID, so uhh, why the extra typing?
This:
SELECT p.Name, o.Quantity FROM Products p, Orders o WHERE o.ProductID = p.ID
Is slightly better than this:
SELECT p.Name, o.Quantity FROM Products p, Orders o WHERE o.ProductID = p.ProductID
Note that both will require table or alias prefixes. But not only am I typing slightly less (multiply that across dozens of tables with long descriptive names and it adds up fast in a data intensive application) but it also makes it easier to know which table is the parent table in every join, which, when joining 8-10 tables in a query, can help quite a bit.
I follow a lot of the same conventions as others here, but I wanted to say a few things that haven't been said yet.
Regardless of whether you like plural names or singular names for your tables, be consistent. Choose one or the other, but don't use both.
The primary key in a table has the same name as the table, with the suffix _PK. Foreign keys have their same name as their corresponding primary key, but with a suffix of _FK. For example, the Product table's primary key is called Product_PK; in the Order table the corresponding foreign key is Product_FK. I picked this habit up from another DBA friend of mine and so far I'm liking it.
Whenever I do an INSERT INTO...SELECT, I alias all the columns in the SELECT portion to match the names of the columns from the INSERT INTO portion to make it easier to maintain and see how things match up.
The most important standard is: don't have a database by default. I find too many developers grabbing a database for projects where life would have been much easier without one (at least yet). It is just a tool in the toolbox, and not every problem is a nail.
Inappropriate use of a database leads to anemic domain models, badly testable code and unneeded performance problems.
I agree with just about everything you have put there except for #5. I often use prefixes for tables and stored procedures because the systems that we develop have lots of different functional areas, so I will tend to prefix the tables and sprocs with an identifier that will allow for them to group nicely in Management Studio based on what area they belong to.
Example: cjso_Users, cjso_Roles, and then you have routing_Users, routing_Roles. This may sound like replication of data, but in reality the two different user/roles tables are for completely separate functions of the system (cjso would be for the customer-based ecommerce app while the routing would stand for employees and distributors who use the routing system).
I like our table naming convention:
People Table
PEO_PersonID
PEO_FirstName
...
Which helps make larger querys a bit more readable. and joins make a bit more sense:
Select * -- naughty!
From People
Join Orders on PEO_PersonID = ORD_PersonID
--...
i guess rather than what the naming convention is, is the consistency of the naming.
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Exact Duplicate
Table Naming Dilemma: Singular vs. Plural Names
Is it better to use singular or plural database table names ? Is there an accepted standard ?
I've heard arguments for and against it, what do you guys think ?
Singular, so you can have:
Customer
CustomerAddress
CustomerAddressAuditTrail
etc.
IMHO, Table names should be plural like Customers.
Class names should be singular like Customer if it maps to a row in Customers table.
I like singular names but appear to be in the minority.
My personal philosophy is that using a plural database table name is redundant, unless you're only planning for the table to contain one row.
I like to use singular names like Agent that have PK names like AgentID.
But that's just me :o)
I like to use plural forms, simply because one table contains several entities, so it seems more natural to me.
Linq to SQL converts plural form table names to singular when creating data entities. I assume that Microsoft would not have implemented this functionality if they considered plural forms for table names bad practice.
At my current company we use Plural for table names. The reasoning is this: If we have a Customers table we consider each row a Customer, so the table itself is a collection of customers.
Well, obviously your database table names have absolutely got to be named in a "standard" fashion which I will hitherto arbitrarily define.
First, all tables names shall be prefixed with "t_". Following this, the singular entity name in StudlyCaps, e.g. "Customer". Immediately afterwards, this shall contain the number of columns created in the first version of the schema, for historical purposes, followed by an underscore, and the precise normal form of the data; either "1", "2", "3" or "B" for BCNF. Any higher normal forms shall be denoted by a "P".
Some examples of acceptable names are:
t_Customer_6_3
t_Order_5_B
t_OrderLine_4_2
I think my point is, it really doesn't matter, as long as the name is reasonably descriptive and naming is consistent.
The most important thing is to be consistent in your usage. It is annoying to have to remember which tables are plurals and which are not. Same thing with your field names, pick one stadard and use it. Don't make the poor developers have to determine if this table uses person_id or personid or peopleid or person$id, etc. It is amazing the amount of time you can waste when you don't have standards trying just to remember which table uses what.
There is no should or must be this way or that way correct answer to this question. It's up to the designer of the database and software.
As for me, I usually use singular names becouse when I do the E-R diagram I have an entity Customer , not Customers, so I keep it same as to not get confused.
Ofcourse some frameworks do favor one style or another, so you should be best of to follow those practices when you notice them.
There are many arguments for each, but it all boils down to what you feel comfortable with. Neither is wrong.
What's really important is that you are consistent. Choose one standard and stick to it, which one you choose is of less importance.
IMHO it doesn't really matter, just do whatever is comfortable with you and the people that are using the database.
I think I subconsciously list main data tables with an s and "pick list" or foreign key tables and singular.
As with lots of these types of questions the best answer is often "consistent". You can argue the table represents a single entity and as such deserves a singular name, or that it contains multiple instances of an entity so it should be plural. My advice is flip a coin and go with it for the entire database (or stick with the convention that already has a majority).
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Academia has it that table names should be the singular of the entity that they store attributes of.
I dislike any T-SQL that requires square brackets around names, but I have renamed a Users table to the singular, forever sentencing those using the table to sometimes have to use brackets.
My gut feel is that it is more correct to stay with the singular, but my gut feel is also that brackets indicate undesirables like column names with spaces in them etc.
Should I stay, or should I go?
I had same question, and after reading all answers here I definitely stay with SINGULAR, reasons:
Reason 1 (Concept). You can think of bag containing apples like "AppleBag", it doesn't matter if contains 0, 1 or a million apples, it is always the same bag. Tables are just that, containers, the table name must describe what it contains, not how much data it contains. Additionally, the plural concept is more about a spoken language one (actually to determine whether there is one or more).
Reason 2. (Convenience). it is easier come out with singular names, than with plural ones. Objects can have irregular plurals or not plural at all, but will always have a singular one (with few exceptions like News).
Customer
Order
User
Status
News
Reason 3. (Aesthetic and Order). Specially in master-detail scenarios, this reads better, aligns better by name, and have more logical order (Master first, Detail second):
1.Order
2.OrderDetail
Compared to:
1.OrderDetails
2.Orders
Reason 4 (Simplicity). Put all together, Table Names, Primary Keys, Relationships, Entity Classes... is better to be aware of only one name (singular) instead of two (singular class, plural table, singular field, singular-plural master-detail...)
Customer
Customer.CustomerID
CustomerAddress
public Class Customer {...}
SELECT FROM Customer WHERE CustomerID = 100
Once you know you are dealing with "Customer", you can be sure you will use the same word for all of your database interaction needs.
Reason 5. (Globalization). The world is getting smaller, you may have a team of different nationalities, not everybody has English as a native language. It would be easier for a non-native English language programmer to think of "Repository" than of "Repositories", or "Status" instead of "Statuses". Having singular names can lead to fewer errors caused by typos, save time by not having to think "is it Child or Children?", hence improving productivity.
Reason 6. (Why not?). It can even save you writing time, save you disk space, and even make your computer keyboard last longer!
SELECT Customer.CustomerName FROM Customer WHERE Customer.CustomerID = 100
SELECT Customers.CustomerName FROM Customers WHERE Customers.CustomerID = 103
You have saved 3 letters, 3 bytes, 3 extra keyboard hits :)
And finally, you can name those ones messing up with reserved names like:
User > LoginUser, AppUser, SystemUser, CMSUser,...
Or use the infamous square brackets [User]
I prefer to use the uninflected noun, which in English happens to be singular.
Inflecting the number of the table name causes orthographic problems (as many of the other answers show), but choosing to do so because tables usually contain multiple rows is also semantically full of holes. This is more obvious if we consider a language that inflects nouns based on case (as most do):
Since we're usually doing something with the rows, why not put the name in the accusative case? If we have a table that we write to more than we read, why not put the name in dative? It's a table of something, why not use the genitive? We wouldn't do this, because the table is defined as an abstract container that exists regardless of its state or usage. Inflecting the noun without a precise and absolute semantic reason is babbling.
Using the uninflected noun is simple, logical, regular and language-independent.
If you use Object Relational Mapping tools or will in the future I suggest Singular.
Some tools like LLBLGen can automatically correct plural names like Users to User without changing the table name itself. Why does this matter? Because when it's mapped you want it to look like User.Name instead of Users.Name or worse from some of my old databases tables naming tblUsers.strName which is just confusing in code.
My new rule of thumb is to judge how it will look once it's been converted into an object.
one table I've found that does not fit the new naming I use is UsersInRoles. But there will always be those few exceptions and even in this case it looks fine as UsersInRoles.Username.
Others have given pretty good answers as far as "standards" go, but I just wanted to add this... Is it possible that "User" (or "Users") is not actually a full description of the data held in the table? Not that you should get too crazy with table names and specificity, but perhaps something like "Widget_Users" (where "Widget" is the name of your application or website) would be more appropriate.
What convention requires that tables have singular names? I always thought it was plural names.
A user is added to the Users table.
This site agrees:
http://vyaskn.tripod.com/object_naming.htm#Tables
This site disagrees (but I disagree with it):
http://justinsomnia.org/writings/naming_conventions.html
As others have mentioned: these are just guidelines. Pick a convention that works for you and your company/project and stick with it. Switching between singular and plural or sometimes abbreviating words and sometimes not is much more aggravating.
How about this as a simple example:
SELECT Customer.Name, Customer.Address FROM Customer WHERE Customer.Name > "def"
vs.
SELECT Customers.Name, Customers.Address FROM Customers WHERE Customers.Name > "def"
The SQL in the latter is stranger sounding than the former.
I vote for singular.
I am of the firm belief that in an Entity Relation Diagram, the entity should be reflected with a singular name, similar to a class name being singular. Once instantiated, the name reflects its instance. So with databases, the entity when made into a table (a collection of entities or records) is plural. Entity, User is made into table Users. I would agree with others who suggested maybe the name User could be improved to Employee or something more applicable to your scenario.
This then makes more sense in a SQL statement because you are selecting from a group of records and if the table name is singular, it doesn't read well.
I stick with singular for table names and any programming entity.
The reason? The fact that there are irregular plurals in English like mouse ⇒ mice and sheep ⇒ sheep. Then, if I need a collection, i just use mouses or sheeps, and move on.
It really helps the plurality stand out, and I can easily and programatically determine what the collection of things would look like.
So, my rule is: everything is singular, every collection of things is singular with an s appended. Helps with ORMs too.
IMHO, table names should be plural like Customers.
Class names should be singular like Customer if it maps to a row in the Customers table.
Singular. I don't buy any argument involving which is most logical - every person thinks his own preference is most logical. No matter what you do it is a mess, just pick a convention and stick to it. We are trying to map a language with highly irregular grammar and semantics (normal spoken and written language) to a highly regular (SQL) grammar with very specific semantics.
My main argument is that I don't think of the tables as a set but as relations.
So, the AppUser relation tells which entities are AppUsers.
The AppUserGroup relation tells me which entities are AppUserGroups
The AppUser_AppUserGroup relation tells me how the AppUsers and AppUserGroups are related.
The AppUserGroup_AppUserGroup relation tells me how AppUserGroups and AppUserGroups are related (i.e. groups member of groups).
In other words, when I think about entities and how they are related I think of relations in singular, but of course, when I think of the entities in collections or sets, the collections or sets are plural.
In my code, then, and in the database schema, I use singular. In textual descriptions, I end up using plural for increased readability - then use fonts etc. to distinguish the table/relation name from the plural s.
I like to think of it as messy, but systematic - and this way there is always a systematically generated name for the relation I wish to express, which to me is very important.
I also would go with plurals, and with the aforementioned Users dilemma, we do take the square bracketing approach.
We do this to provide uniformity between both database architecture and application architecture, with the underlying understanding that the Users table is a collection of User values as much as a Users collection in a code artifact is a collection of User objects.
Having our data team and our developers speaking the same conceptual language (although not always the same object names) makes it easier to convey ideas between them.
I personaly prefer to use plural names to represent a set, it just "sounds" better to my relational mind.
At this exact moment i am using singular names to define a data model for my company, because most of the people at work feel more confortable with it.
Sometimes you just have to make life easier to everyone instead of imposing your personal preferences.
(that's how i ended up in this thread, to get a confirmation on what should be the "best practice" for naming tables)
After reading all the arguing in this thread, i reached one conclusion:
I like my pancakes with honey, no matter what everybody's favorite flavour is. But if i am cooking for other people, i will try to serve them something they like.
Singular. I'd call an array containing a bunch of user row representation objects 'users', but the table is 'the user table'. Thinking of the table as being nothing but the set of the rows it contains is wrong, IMO; the table is the metadata, and the set of rows is hierarchically attached to the table, it is not the table itself.
I use ORMs all the time, of course, and it helps that ORM code written with plural table names looks stupid.
I've actually always thought it was popular convention to use plural table names. Up until this point I've always used plural.
I can understand the argument for singular table names, but to me plural makes more sense. A table name usually describes what the table contains. In a normalized database, each table contains specific sets of data. Each row is an entity and the table contains many entities. Thus the plural form for the table name.
A table of cars would have the name cars and each row is a car. I'll admit that specifying the table along with the field in a table.field manner is the best practice and that having singular table names is more readable. However in the following two examples, the former makes more sense:
SELECT * FROM cars WHERE color='blue'
SELECT * FROM car WHERE color='blue'
Honestly, I will be rethinking my position on the matter, and I would rely on the actual conventions used by the organization I'm developing for. However, I think for my personal conventions, I'll stick with plural table names. To me it makes more sense.
I don't like plural table names because some nouns in English are not countable (water, soup, cash) or the meaning changes when you make it countable (chicken vs a chicken; meat vs bird).
I also dislike using abbreviations for table name or column name because doing so adds extra slope to the already steep learning curve.
Ironically, I might make User an exception and call it Users because of USER (Transac-SQL), because I too don't like using brackets around tables if I don't have to.
I also like to name all the ID columns as Id, not ChickenId or ChickensId (what do plural guys do about this?).
All this is because I don't have proper respect for the database systems, I am just reapplying one-trick-pony knowledge from OO naming conventions like Java's out of habit and laziness. I wish there were better IDE support for complicated SQL.
We run similar standards, when scripting we demand [ ] around names, and where appropriate schema qualifiers - primarily it hedges your bets against future name grabs by the SQL syntax.
SELECT [Name] FROM [dbo].[Customer] WHERE [Location] = 'WA'
This has saved our souls in the past - some of our database systems have run 10+ years from SQL 6.0 through SQL 2005 - way past their intended lifespans.
If we look at MS SQL Server's system tables, their names as assigned by Microsoft are in plural.
The Oracle's system tables are named in singular. Although a few of them are plural.
Oracle recommends plural for user-defined table names.
That doesn't make much sense that they recommend one thing and follow another.
That the architects at these two software giants have named their tables using different conventions, doesn't make much sense either... After all, what are these guys ... PhD's?
I do remember in academia, the recommendation was singular.
For example, when we say:
select OrderHeader.ID FROM OrderHeader WHERE OrderHeader.Reference = 'ABC123'
maybe b/c each ID is selected from a particular single row ...?
The system tables/views of the server itself (SYSCAT.TABLES, dbo.sysindexes, ALL_TABLES, information_schema.columns, etc.) are almost always plural. I guess for the sake of consistency I'd follow their lead.
I am a fan of singular table names as they make my ER diagrams using CASE syntax easier to read, but by reading these responses I'm getting the feeling it never caught on very well? I personally love it. There is a good overview with examples of how readable your models can be when you use singular table names, add action verbs to your relationships and form good sentences for every relationships. It's all a bit of overkill for a 20 table database but if you have a DB with hundreds of tables and a complex design how will your developers ever understand it without a good readable diagram?
http://www.aisintl.com/case/method.html
As for prefixing tables and views I absolutely hate that practice. Give a person no information at all before giving them possibly bad information. Anyone browsing a db for objects can quite easily tell a table from a view, but if I have a table named tblUsers that for some reason I decide to restructure in the future into two tables, with a view unifying them to keep from breaking old code I now have a view named tblUsers. At this point I am left with two unappealing options, leave a view named with a tbl prefix which may confuse some developers, or force another layer, either middle tier or application to be rewritten to reference my new structure or name viewUsers. That negates a large part of the value of views IMHO.
Tables: plural
Multiple users are listed in the users table.
Models: singular
A singular user can be selected from the users table.
Controllers: plural
http://myapp.com/users would list multiple users.
That's my take on it anyway.
I once used "Dude" for the User table - same short number of characters, no conflict with keywords, still a reference to a generic human. If I weren't concerned about the stuffy heads that might see the code, I would have kept it that way.
I've always used singular simply because that's what I was taught. However, while creating a new schema recently, for the first time in a long time, I actively decided to maintain this convention simply because... it's shorter. Adding an 's' to the end of every table name seems as useless to me as adding 'tbl_' in front of every one.
This may be a bit redundant, but I would suggest being cautious. Not necessarily that it's a bad thing to rename tables, but standardization is just that; a standard -- this database may already be "standardized", however badly :) -- I would suggest consistency to be a better goal given that this database already exists and presumably it consists of more than just 2 tables.
Unless you can standardize the entire database, or at least are planning to work towards that end, I suspect that table names are just the tip of the iceberg and concentrating on the task at hand, enduring the pain of poorly named objects, may be in your best interest --
Practical consistency sometimes is the best standard... :)
my2cents ---
As others have mentioned here, conventions should be a tool for adding to the ease of use and readability. Not as a shackle or a club to torture developers.
That said, my personal preference is to use singular names for both tables and columns. This probably comes from my programming background. Class names are generally singular unless they are some sort of collection. In my mind I am storing or reading individual records in the table in question, so singular makes sense to me.
This practice also allows me to reserve plural table names for those that store many-to-many relationships between my objects.
I try to avoid reserved words in my table and column names, as well. In the case in question here it makes more sense to go counter to the singular convention for Users to avoid the need to encapsulate a table that uses the reserved word of User.
I like using prefixes in a limited manner (tbl for table names, sp_ for proc names, etc), though many believe this adds clutter. I also prefer CamelBack names to underscores because I always end up hitting the + instead of _ when typing the name. Many others disagree.
Here is another good link for naming convention guidelines: http://www.xaprb.com/blog/2008/10/26/the-power-of-a-good-sql-naming-convention/
Remember that the most important factor in your convention is that it make sense to the people interacting with the database in question. There is no "One Ring to Rule Them All" when it comes to naming conventions.
Possible alternatives:
Rename the table SystemUser
Use brackets
Keep the plural table names.
IMO using brackets is technically the safest approach, though it is a bit cumbersome. IMO it's 6 of one, half-a-dozen of the other, and your solution really just boils down to personal/team preference.
My take is in semantics depending on how you define your container. For example, A "bag of apples" or simply "apples" or an "apple bag" or "apple".
Example:
a "college" table can contain 0 or more colleges
a table of "colleges" can contain 0 or more collegues
a "student" table can contain 0 or more students
a table of "students" can contain 0 or more students.
My conclusion is that either is fine but you have to define how you (or people interacting with it) are going to approach when referring to the tables; "a x table" or a "table of xs"
I think using the singular is what we were taught in university. But at the same time you could argue that unlike in object oriented programming, a table is not an instance of its records.
I think I'm tipping in favour of the singular at the moment because of plural irregularities in English. In German it's even worse due to no consistent plural forms - sometimes you cannot tell if a word is plural or not without the specifying article in front of it (der/die/das). And in Chinese languages there are no plural forms anyway.
I only use nouns for my table names that are spelled the same, whether singular or plural:
moose
fish
deer
aircraft
you
pants
shorts
eyeglasses
scissors
species
offspring
I did not see this clearly articulated in any of the previous answers. Many programmers have no formal definition in mind when working with tables. We often communicate intuitively in terms of of "records" or "rows". However, with some exceptions for denormalized relations, tables are usually designed so that the relation between the non-key attributes and the key constitutes a set theoretic function.
A function can be defined as a subset of a cross-product between two sets, in which each element of the set of keys occurs at most once in the mapping. Hence the terminology arising from from that perspective tends to be singular. One sees the same singular (or at least, non-plural) convention across other mathematical and computational theories involving functions (algebra and lambda calculus for instance).
I always thought that was a dumb convention. I use plural table names.
(I believe the rational behind that policy is that it make it easier for ORM code generators to produce object & collection classes, since it is easier to produce a plural name from a singular name than vice-versa)
I have a table in a DB (Postgres based), which acts like a superclass in object-oriented programming. It has a column 'type' which determines, which additional columns should be present in the table (sub-class properties). But I don't want the table to include all possible columns (all properties of all possible types).
So I decided to make a table, containg the 'key' and 'value' columns (i.e. 'filename' = '/file', or 'some_value' = '5'), which contain any possible property of the object, not included in the superclass table. And also made one related table to contain the available 'key' values.
But there is a problem with such architecture - the 'value' column should be of a string data type by default, to be able to contain anything. But I don't think converting to and from strings is a good decision. What is the best way to bypass this limitation?
The design you're experimenting with is a variation of Entity-Attribute-Value, and it comes with a whole lot of problems and inefficiencies. It's not a good solution for what you're doing, except as a last resort.
What could be a better solution is what fallen888 describes: create a "subtype" table for each of your subtypes. This is okay if you have a finite number of subtypes, which sounds like what you have. Then your subtype-specific attributes can have data types, and also a NOT NULL constraint if appropriate, which is impossible if you use the EAV design.
One remaining weakness of the subtype-table design is that you can't enforce that a row exists in the subtype table just because the main row in the superclass table says it should. But that's a milder weakness than those introduced by the EAV design.
edit: Regarding your additional information about comments-to-any-entity, yes this is a pretty common pattern. Beware of a broken solution called "polymorphic association" which is a technique many people use in this situation.
How about this instead... each sub-type gets its own DB table. And the base/super table just has a varchar column that holds the name of the sub-type DB table. Then you can have something like this...
Entity
------
ID
Name
Type
SubTypeName (value of this column will be 'Dog')
Dog
---
VetName
VetNumber
etc
If you don't want your (sub-)table names to be varchar values in the base table, you can also just have a SubType table whose primary key will be in the base table.
The only workaround (while retaining your strucure) is to have separate tables:
create table IntProps(...);
create table StringProps(...);
create table CurrencyProps(...);
But I do not think that this is a good idea...
One common approach is having the key-value table contain multiple columns, one for each data type, i.e. StringValue, DecimalValue, etc.
Just know you're trading queryability and performance for a database schema you don't need to change. You could also consider ORM mapping or an object database.
You could have a per type key/value table. The available table would need to encode the availability of a specific key/type pair to point to the correctly typed key/value table.
This seems like a highly inefficient architecture in for a row based relational databases however.
Perhaps you should take a look at a column oriented relational database?
Thanks for the answers. I'll explain a little bit more specifically what i need.
There's a need to program a blog+forum website, and I've been looking at the WordPress DB structure.
There's a strong need for the ability to place comments to any kind of 'object', like a blog entry, or a video file attachment to it. The above DB structure being very easy to scale and to fulfill all our needs was the reason of its choice.
But that's not late to change it, cause this is in stage of early engineering. Also our model smells now like a completely tree-hierarchy based DB. For now I'll accept Bill Karwin's and fallen888 answers, but maybe I'm going in a totally wrong direction?
about the user being able to add a new field to the table:
I admire all these people making comments.
I used to be interested in this kind of thing a few years ago, but have written little code recently (apart from a little bit of PHP and MYSQL).
I think it's fine if you want to keep going - you may end up with something new.
Sorry to pour any cold water on the scheme - I admire your efforts. My personal belief is that if you go far enough in this direction, you will end up with a system that interprets more of natural language than SQL does. (Around 1970, SQL was actually spelt Sequel, and it actually stood for "structured english query language", but after they standardized it in the 1970's - I think someone said that Oracle was the first commercial implementation, 19079, the "English" got dropped off, because I guess they decided that it was only a tiny subset of English.
I have run out of steam in this area, because I haven't got a job. Without an easy job that pays the bills, where I can experiment with these ideas, it's a bit hard to concentrate on this area.
Best wishes to all.
sorry, I wrote 19079 above, I meant the year 1979. Oracle got their first contract writing a database for the CIA.