考虑下面的 PL/SQL 代码，这段代码生成一个 XML 格式的矩阵样式的报表： declare l_count integer. begin dbms_output.put_line( ). -- generate matrix of parts by country for part in (0select id,description from parts order by description) loop dbms_output.put_line( ). dbms_output.put_line( ||part.description|| ). for country in (0select code from countries order by name) loop 0select sum(cnt) into l_count from orders where part_id = part.id and cc = country.code. dbms_output.put_line( ||nvl(l_count,0)|| ). end loop. dbms_output.put_line( ). end loop. dbms_output.put_line( ). end. 如果在这个例子中 parts 和 countries 有很多行数据，那么性能就会趋于下降。这是因为，在 PL/SQL 中，每次遇到一个游标 FOR 循环，在重新查询并获得数据时，都会有一个切换到 SQL 的上下文切换。 以一些服务器端内存为代价，提高这种构造的速度是有可能做到的——如果动态构建 PL/SQL 数据表和矩阵单元格条目就可以提高速度。例如： declare type part_tbl_type is table of parts%rowtype index by binary_integer. part_tbl part_tbl_type. -- type country_tbl_type is table of countries%rowtype index by binary_integer. country_tbl country_tbl_type. -- type cell_rec is record ( part_id orders.part_id%type, cc orders.cc%type, cnt orders.cnt%type ). type cell_tbl_type is table of cell_rec index by binary_integer. cell_tbl cell_tbl_type. -- i pls_integer. begin -- build rows for row in (0select * from parts order by description) loop part_tbl(part_tbl.count 1) := row. end loop. -- build columns for col in (0select * from countries order by name) loop country_tbl(country_tbl.count 1) := col. end loop. -- build cells for cell in (0select part_id,cc,sum(cnt) from orders group by part_id,cc) loop cell_tbl(cell_tbl.count 1) := cell. end loop. dbms_output.put_line( ). -- generate matrix of parts by country i := cell_tbl.first. for row in part_tbl.first .. part_tbl.last loop dbms_output.put_line( ). dbms_output.put_line( ||part_tbl(row).description|| ). for col in country_tbl.first .. country_tbl.last loop if cell_tbl(i).part_id = part_tbl(row).id and cell_tbl(i).cc = country_tbl(col).code