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使用查询改写提高查询性能
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编辑：华夏媒体 作者：未知 来源：网络 时间：2006-07-29 总浏览量：5450 |
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)
ATTRIBUTE time_key determines (day_of_week, holiday)
ATTRIBUTE month determines (month_name);
现在，如果具有清单 4中要求按年的销售额的查询，你仍然可以使用monthly_sales_mv物化视图，因为维度对象中的HIERARCHY子句告诉Oracle数据库月销售额可以积累成年销售额。它利用前面描述的joinback技巧由物化视图中的“月”列得到“年”列的值。
代码清单 4：通过joinback和HIERARCHY获得销售总额
SELECT t.year, p.category, SUM(ps.purchase_price) as sum_of_sales
FROM time t, product p, purchases ps
WHERE t.time_key = ps.time_key AND
ps.product_id = p.product_id
GROUP BY t.year, p.category;
Id Operation Name
__________________________________________________
0 SELECT STATEMENT
1 SORT GROUP BY
2 HASH JOIN
3 HASH JOIN
4 VIEW
5 SORT UNIQUE
6 TABLE ACCESS FULL TIME
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