[dba-SQLServer] TSQL IF in a non-standard way

[John W. Colby]

I am writing a stored procedure which uses "cascading" CTEs to grab a 
raw data set, and then transform that raw data set.  For example I need 
"All the addressed in a table" joined to "all the addresses in another 
table".  Simple enough.

Then I do transforms looking for distances between the addresses in the 
two tables.  Also simple enough.

But Now sometimes I just need all addresses, sometimes I need only 
"specific counties" or "specific MSA numbers" or "specific states". I 
have to pull data from a CSV, a county list, or a state list, or an MSA 
list.

What I am thinking is use an IF or switch to return a result set from a 
select.

If @Selector = 'ST' Select XYZ else if @Selector = 'MSA' Select ABC

Etc.

This doesn't seem to work, or at least I can't find examples of this 
kind of use.  IF seems to be used in TSQL to return specific values in 
fields inside of a select statement.

Any suggestions for how to implement this?

-- 
John W. Colby