PEAR's implementation of sequences does not allow cross-database sequences for DBMSes which allow x-db queries. For example, with MySQL, cross-database queries are allowed, but one can't do

 $new_id = $SQL->nextId("database2.table");

because the dot (.) in sequence name is translated into underscore (_), which results in sequence name of "database.database2_table_seq", which is NOT the intended result.