Thursday, May 13, 2010

Database Standards Part II: Schemas, Tables & View and Columns

This is Part 2 of 6 blogs about database standards we use at my current employer. Repeating myself, though we do not enforce these with an iron fist, they are advised for clarity and consistency. The important point, in my opinion, is establish a set of standards and stick to them.

Schema

The seperation of schmea name and logins was a great addition in SQL Server 2005. Schema names should be used in place of dbo. This makes viewing in SSMS great with filters. It also categorizes the objects so a new DBA or developer can get a good view of the organization in a database. We suggest a Common schema for objects that do not fit in a group, then names that are specific to functionality - Payroll, HR, Billing, etc.

Tables
Tables names should reflect its functionality and they cannot start with a number, contain spaces, underscores or be reserved words. ANSI_NULL (OFF is deprecated in a future version) should be SET ON. Pascal Casing should be used like ClientBill and singular like Admit not Admits.

There are 3 different kinds of Lookup tables we see - developer populated (workflow), small lists (state) and known list that are updattable (RevenueCode). Small lookup tables can use a character primary key. If the developer insists on ID (identity), then a character code/description column created with a unique contraint must be included. The code should be used in the transaction table. (I will clarify this is a seperate blog). Lookup tables use camel case - lkState.

The transaction table(s) should use a ID (indentity or sequential int) as the primary, but should have a unique contraint for uniquely identifying a row. Third Key Normal Form and higher is required. The ID field will be the foreign key in the child table, and named ID (PatientID in an Episode table).

Views
Camel casing should be used in naming views - vwPatientEpisode. Future thinking should be used if the view will eventually become an indexed view, then schema binging and ansi settings need to be looked at.

Columns
Column names should describe the data placed in them, using Pascal Casing - LastName and not start with a number/special character, no spaces, dashes or underscores. Beware of reserve words or key words as object names. Do not repeat table name - use LastName not PatientLastName unless a foreign key to another table - PatientID. No data type in the name - intPatientCount, but Date is acceptable in a date name - AdmitDate.

Be aware of new features in 2008 like a seperate DATE and TIME data types. Before, you had to use midnight as the time in a date column type in order to not specify a time.

Repeating
Though my opinion is not the same as some of these standards (I say you can abbrev. anything), I do believe standards should be discussed and established, then followed. IF a deviation is needed, a group discussion should be voted on to change.


Next week I will talk about Indexes, constraints and Primary/Foreigh Keys.


Thomas LeBlanc

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