The execute statement returns 0E0 if no records were affected/returned. Instead of :

if($rs1 != 'NULL')
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Try:

if($rs1 ne "0E0")
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Also, I'm pretty sure the != test is for numeric values only.

From the MySQL Reference Manual:
If no rows are affected, execute returns "0E0" , which Perl treats as zero but regards as true. If an error occurs, execute returns undef.