You can place your logic in a CTE and then use your WHERE clause when selecting from the CTE.
Probably not the best solution but still an option

What does your query look like so far?
ie. What have you tried?

SQL Server's builtin "big data" functionality is actually something called Polybase.
Polybase allows users to interface with HDFS (Hadoop Distributed File System) which is the storage layer for a Hadoop...

The issue is with construction of the dynamic SQL.

If you look at this section as an example:

StartDateTime >= ' + @StartDate + '

I don't think you can dynamically use the parameter like that.
You'll have to build your sql statement dynamically like this:

DECLARE @pDB AS VARCHAR(10)
DECLARE

There are a few suggestions here:
https://www.mssqltips.com/sqlservertip/3171/identify-sql-server-databases-that-are-no-longer-in-use/

Have a look at some of the suggestions in this link:
https://www.sqlservercentral.com/Forums/Topic1556669-148-1.aspx

Does your destination table already contain data?
If so, maybe you could import your data into a staging heap table first (empty table with no indexes)

I have been wondering about how a SQL instance should be set up properly on a VM.
With physical drives you would put your data and log files on separate...

I wouldn't nest a select statement like that.
Rather do another outer join:

select A.name
  ,(Case WHEN A.id = 2 then C.ID ELSE ??? END)
from...

Although you'll get better performance by flattening everything into one table / view, the users' experience might not be as great.
The data might make better sense if attributes are...

Maybe this is the LIKE syntax you are looking for as in this example:

DECLARE @String AS VARCHAR(7)

SET @String = '33AA5CV'

SELECT CASE...

The "Import Flat File" feature is quite new, and I'm not sure if it resolves collation issues, but maybe worth trying:
http://www.sqlservercentral.com/blogs/discussionofsqlserver/2017/10/11/new-features-in-ssms-173/

Hi Sam, have a look at this article about the OUTPUT clause of a merge statement:
http://www.sqlservercentral.com/articles/T-SQL/156901/
Hopefully it'll help with what you are trying to achieve.