Conversion Failed Varchar to Date with TOP and WHERE - sql-server

Question

I've got a MSSQL 2012 server that holds olders databases (day by day) of my ERP. Simple JOB restores a newest databases from my backup server and removes the oldest one's. It was working fine for few months, but a week ago it started to fail. One of the queries returns: 'Conversion failed when converting date and/or time from character string.'
All database have the same schema for a name 'DATABASE_date' ex.: 'DATABASE_20150224'.
This is the query:
SELECT TOP 1 name
from sys.databases
where name like 'DataBaseName_%'
order by CAST(right(name,8) as DATE)
IF i remove 'TOP 1' it works fine.
SELECT name
from sys.databases
where name like 'DataBaseName_%'
order by CAST(right(name,8) as DATE)
It seems like MSSQL check's all databases on this server (2 new databases of a different app). But why? There's a 'WHERE' cluase and simple select works just fine.

Answer 1

SQL is a declarative language. A database is free to first order the rows and then filter them, or the other way around.
You are relaying on a where clause to filter out rows that would cause an exception in your string manipulation expression. But SQL Server can run the where after the order by.
One approach is bullet-proofing the order by:
order by
case
when name not like 'DataBaseName_%' then name
else CAST(right(name,8) as DATE)
end
Note that even this isn't 100% guaranteed to work. SQL Server could legally evaluate both sides of the case and throw away the second one.