From perlfaq4 - How do I sort an array by (anything)?:

If you need to sort on several fields, the following paradigm is useful.

    @sorted = sort { field1($a) <=> field1($b) ||
                     field2($a) cmp field2($b) ||
                     field3($a) cmp field3($b)
                   } @data;
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(Also, it's "Perl", not "PERL")

To apply this code to the data structure as given by the op, this gives:

    @sorted = sort { $a->{key2} cmp $b->{key2} ||
                     $a->{num1} <=> $b->{num1} ||
                     $a->{key3} cmp $b->{key3} ||
                   } @data;
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Note that to sort descending for one column, just swap $a and $b in the comparison expression, for that column.