The documentation is pretty clear:
Generally, you can only rely on a row count after a non-SELECT execute (for some specific operations like UPDATE and DELETE), or after fetching all the rows of a SELECT statement.

You called ->rows before fetching all the rows. 

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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In reply to Re: DBD::Sybase $sth->rows returns -1 by choroba
in thread DBD::Sybase $sth->rows returns -1 by Perl300

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