Thursday, June 17, 2010

Database Standards Part V: Triggers and User-defined Functions

Database Standards Part V: Triggers and User-defined Functions

This is Part 5 of 6 blogs about database standards. Again, though we do not enforce these with an iron fist, they are advised for clarity and consistency. The important point, in my opinion, is to establish a set of standards and stick to them.
Naming convention for triggers are 'it' for insert, 'ut' for update and dt for delete (itPatient). Trigger can slow CRUD statements so we warn developers to be careful when creating triggers. It also can 'hide' logic from development. Over and over, we get confused people trying to find how data gets added to a table because of a trigger on another table. Verify during a review that the trigger can handle multi-row updates when joining to the inserted or deleted recordsets. Most triggers I see are related to auditing Ins/Upd/Del statements.
User-Defined Functions
User-defined functions are prefixed with udf. They can be helpful with string manipulation commonly used in stored procedures or SQL statements. UDFs do add processing time to the execution and can cause scans when used on fields in a WHERE clause. Looking at an execution plan might exclude the code from the UDF. I see table-valued UDFs used like DMFs from dynamic management objects from Microsoft, mostly on small data sets.
Also, when  profiling, you get a statement for each call to the udf for each row in the SELECT statement if used in a query, so you might want to exclude the data in the profiled output.
Repeating again, and again…

Though my opinion is not the same as some of these standards, 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 coding and deisgn standards.

Thomas LeBlanc

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