How can I set up a simple calculated field in SQL Server?

Question

I have a table with several account fields like this:

MAIN_ACCT
GROUP_ACCT
SUB_ACCT

I often need to combine them like this:

SELECT MAIN_ACCT+'-'+GROUP_ACCT+'-'+SUB_ACCT
FROM ACCOUNT_TABLE

I'd like a calculated field that automatically does this, so I can just say:

SELECT ACCT_NUMBER FROM ACCOUNT_TABLE

What is the best way to do this?

I'm using SQL Server 2005.

Answer 1

ALTER TABLE ACCOUNT_TABLE 
ADD ACCT_NUMBER AS MAIN_ACCT+'-'+GROUP_ACCT+'-'+SUB_ACCT PERSISTED

This will persist a calculated column and may perform better in selects than a calculation in view or UDF if you have a large number of records (once the intial creation of the column has happened which can be painfully slow and should probably happen during low usage times). It will slow down inserts and updates. Usually I find a slow insert or update is tolerated better by users than a delay in a select unless you get locking issues.

The best method for doing this will depend a great deal on your usage and what kind of performance you need. If you don't have a lot of records or if the computed column won't be called that frequently, you may not want a persisted column, but if you are frequently running reports with all the records for the year or other large sets of data, you may find the persisted calculated column works better for you. As with any task of this nature, the only way to know what works best in your situation is to test.