相关疑难解决方法(0)

我station_logs在 PostgreSQL 9.6 数据库中有一个表：

    Column     |            Type             |    
---------------+-----------------------------+
 id            | bigint                      | bigserial
 station_id    | integer                     | not null
 submitted_at  | timestamp without time zone | 
 level_sensor  | double precision            | 
Indexes:
    "station_logs_pkey" PRIMARY KEY, btree (id)
    "uniq_sid_sat" UNIQUE CONSTRAINT, btree (station_id, submitted_at)

我试图level_sensor根据submitted_at, 对于每个station_id. 大约有 400 个唯一station_id值，每个station_id.

创建索引之前：

EXPLAIN ANALYZE
SELECT DISTINCT ON(station_id) station_id, submitted_at, level_sensor
FROM station_logs ORDER BY station_id, submitted_at DESC;

 唯一（成本=4347852.14..4450301.72行=89宽度=20）（实际时间=22202.080..27619.167行=98循环=1）
   -> Sort …