简化表:
CREATE TABLE products (
product_no integer PRIMARY KEY,
sales integer,
status varchar(16),
category varchar(16));
CREATE INDEX index_products_sales ON products (sales);
CREATE INDEX index_products_status ON products (status);
CREATE INDEX index_products_category ON products (category);
PostgreSQL 版本是 8.4。列“状态”和“类别”
有 2000 万个产品/行分布在 15 个类别中。
最常用的查询之一是获取最畅销的三种产品,不包括类别“cat3”和“cat7”中的产品:
SELECT product_no, sales
FROM products
WHERE status = 'something' AND category NOT IN ('cat3', 'cat7')
ORDER BY sales DESC
LIMIT 3;
Limit (cost=0.00..8833.39 rows=3 width=12) (actual time=9235.332..9356.284 rows=3 loops=1)
-> Index Scan using index_products_sales on products (cost=0.00..68935806.85 rows=23412 width=12) (actual time=9235.327..9356.278 rows=3 loops=1)
Filter: (((category)::text <> ALL ('{cat3,cat7}'::text[])) AND ((status)::text = 'something'::text))
使这个特定查询运行得更快的最佳索引是什么?