I'll give you the best explanation I can of the Perl part:
Assuming $dbh is a database handle and you're using DBI, it attempts to prepare a sql statement

if exists(select 1 from INFORMATION_SCHEMA
+.tables where table_name = 'DSR_SMR_Result_storage_keep') begin DROP 
+TABLE DSR_SMR_Result_storage_keep  end
[download]

and gives an error if it can't prepare it.

It does so by 1) setting the sql statement to a scalar variable, 2) declaring another scalar, and 3) using a previously prepared database handle to prepare the sql statement.

Of course, you don't actually need to know much Perl to know that; I'm sure anyone who worked in any language could tell you that. I'd suspect you yourself knew that already.

That's why people keep telling you you're not asking Perl questions. If my answer above was actually helpful, maybe you really are having Perl problems. If not, you should go to some other forum with this stuff. Believe it or not, generally Sql Server experts know more about T-SQL than Perl experts (not that I'm claiming particular expertise), and you'd get far better answers to your questions.