Question

此处继续其他问题：

How to get date_part query to hit index?

执行以下查询时，它会击中我在datelocal，视图，印象，性别，年龄组字段上创建的复合索引：

SELECT date_part('hour', datelocal)                AS hour
     , SUM(views) FILTER (WHERE gender = 'male')   AS male
     , SUM(views) FILTER (WHERE gender = 'female') AS female
FROM   reportimpression
WHERE  datelocal >= '2019-02-01' AND datelocal <  '2019-03-01'
GROUP  BY 1
ORDER  BY 1;

但是，我也希望能够基于WHERE中的其他子句来过滤此查询，例如：

SELECT date_part('hour', datelocal)                AS hour
     , SUM(views) FILTER (WHERE gender = 'male')   AS male
     , SUM(views) FILTER (WHERE gender = 'female') AS female
FROM   reportimpression
WHERE  datelocal >= '2019-02-01' AND datelocal <  '2019-03-01'
AND network LIKE '%'
GROUP  BY 1
ORDER  BY 1;

第二个查询要比第一个查询慢很多，尽管它不会对我的索引产生影响，但是它应该对更少的记录进行操作。

表架构：

CREATE TABLE reportimpression (
    datelocal timestamp without time zone,
    devicename text,
    network text,
    sitecode text,
    advertisername text,
    mediafilename text,
    gender text,
    agegroup text,
    views integer,
    impressions integer,
    dwelltime numeric
);

-- Indices -------------------------------------------------------

CREATE INDEX reportimpression_datelocal_index ON reportimpression(datelocal timestamp_ops);
CREATE INDEX reportimpression_viewership_index ON reportimpression(datelocal timestamp_ops,views int4_ops,impressions int4_ops,gender text_ops,agegroup text_ops);
CREATE INDEX reportimpression_test_index ON reportimpression(datelocal timestamp_ops,(date_part('hour'::text, datelocal)) float8_ops);

分析输出：

Finalize GroupAggregate  (cost=1005368.37..1005385.70 rows=3151 width=24) (actual time=70615.636..70615.649 rows=24 loops=1)
  Group Key: (date_part('hour'::text, datelocal))
  ->  Sort  (cost=1005368.37..1005369.94 rows=3151 width=24) (actual time=70615.631..70615.634 rows=48 loops=1)
        Sort Key: (date_part('hour'::text, datelocal))
        Sort Method: quicksort  Memory: 28kB
        ->  Gather  (cost=1005005.62..1005331.75 rows=3151 width=24) (actual time=70615.456..70641.208 rows=48 loops=1)
              Workers Planned: 1
              Workers Launched: 1
              ->  Partial HashAggregate  (cost=1004005.62..1004016.65 rows=3151 width=24) (actual time=70613.132..70613.152 rows=24 loops=2)
                    Group Key: date_part('hour'::text, datelocal)
                    ->  Parallel Seq Scan on reportimpression  (cost=0.00..996952.63 rows=2821195 width=17) (actual time=0.803..69876.914 rows=2429159 loops=2)
                          Filter: ((datelocal >= '2019-02-01 00:00:00'::timestamp without time zone) AND (datelocal < '2019-03-01 00:00:00'::timestamp without time zone) AND (network ~~ '%'::text))
                          Rows Removed by Filter: 6701736
Planning time: 0.195 ms
Execution time: 70641.349 ms

我是否需要创建其他索引，调整SELECT或完全其他？

Answer 1

您添加的谓词使用LIKE运算符：

AND network LIKE '%'

实际查询计划取决于您通过的内容而不是'％'。但是，通常，纯btree索引对此没有用。您将需要一个三字母组合索引或使用文本搜索基础结构或类似的结构，具体取决于您要寻找的模式。

请参阅：

您甚至可以结合使用多种索引策略。示例：

PostgreSQL: Find sentences closest to a given sentence

如果应该这样：

AND network = '<input_string>'

然后，一定要使用 = 运算符，而不是LIKE。重要性升序的原因：

更短
减少混乱
使Postgres规划器的工作更简单（非常便宜）
正确

如果不经意传递带有特殊字符的字符串，则可能会得到错误的结果。参见：
- Escape function for regular expression or LIKE patterns

WHERE子句不同组合的索引策略，包括文字样式

1 个答案: