Yes - like that - you're almost there :-)

The variables $fieldname, $fieldtype and $fieldlength are lexically scoped (with my) and do not exist outside of the for loop. This is good - don't change that bit.

You'll need to build your query as you iterate through the for loop. Start the process before you enter the loop:

...
my $query = "CREATE TABLE $table";
for ($f=1;$f<=$field;$f++)
...
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Now, on each pass through the loop, add the appropriate syntax for each column after you've gathered the data:

    my $fieldname=param('fieldname' .$f);
    my $fieldtype=param('fieldtype' .$f);
    my $fieldlength=param('fieldlength' .$f);
    $query .= "...
}
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When you exit the loop, $query should contain your complete CREATE TABLE statement.