In addition to the excellent answers provided by corion, ysth & moritz, I may I suggest the use of a different delimiter for the 'q' operator - it took me a while to read

my $str = q{CALL DB_PROC_FOO(} . join(q{,}, @qm) . q{)};
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...the braces and parens looked alike until I looked really close ... compare with

my $str = q/CALL DB_PROC_FOO(/ . join(q/,/, @qm) . q/)/;
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where confusion of braces and parens is, IMO, somewhat reduced.