Quote

$rv = $sth->rows;

Returns the number of rows affected by the last row affecting command, or -1 if the number of
rows is not known or not available.

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.

Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live. -- Damian Conway in "Perl Best Practices"
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