我不敢相信我看到的带有 ORDER BY 子句的简单选择。 这是我的查询和错误的结果:
SELECT date_valid, id_variable FROM myTable
WHERE id_stn='78224' AND date_valid BETWEEN '2014-07-03 09:00:00'
AND '2014-07-03 21:00:00' AND id_variable IN (11012,12004)
ORDER BY date_valid ;
date_valid | id_variable
---------------------+-------------
2014-07-03 09:00:00 | 11012
2014-07-03 15:00:00 | 11012
2014-07-03 21:00:00 | 11012
2014-07-03 09:00:00 | 12004
2014-07-03 15:00:00 | 12004
2014-07-03 21:00:00 | 12004
如您所见,排序似乎是在 id_variable 而不是 date_valid 上完成的。为了获得预期的结果,我必须创建一个 Postgresql 无法优化的新字段或提供超过 1 天的时间戳范围:
SELECT date_valid,id_variable FROM myTable
WHERE id_stn='78224' AND date_valid BETWEEN '2014-07-03 09:00:00'
AND '2014-07-03 21:00:00' AND id_variable IN (11012,12004)
ORDER BY date_valid + '0 hours'::INTERVAL;
date_valid | id_variable
---------------------+-------------
2014-07-03 09:00:00 | 11012
2014-07-03 09:00:00 | 12004
2014-07-03 15:00:00 | 11012
2014-07-03 15:00:00 | 12004
2014-07-03 21:00:00 | 11012
2014-07-03 21:00:00 | 12004
这是一个部分表定义,它按每个月的 date_valid 进行分区:
Column | Type
---------------+-----------------------------
id_obs | bigint
date_valid | timestamp without time zone
id_variable | integer
id_stn | character varying(50)
Indexes:
"myTable_pkey" PRIMARY KEY, btree (id_obs)
"myTable_ukey" UNIQUE CONSTRAINT, btree (date_valid, id_variable, lat, lon)
Check constraints:
"myTable_date_valid_check" CHECK (date_valid >= '2014-07-01 00:00:00'::timestamp without time zone AND date_valid < '2014-08-01 00:00:00'::timestamp without time zone)
Triggers:
myTable_before_update BEFORE UPDATE ON myTable_201407 FOR EACH ROW EXECUTE PROCEDURE obs_update()
Inherits: myTable_parent
Has OIDs: no
如果结果是在同一天,Postgresql 不会按小时排序,这似乎是一个错误。这一定是优化器问题,因为如果我在另一个未编制索引的时间戳字段上排序,我不会遇到这个问题。如果我在每个日期字符串之后指定::TIMESTAMP,或者如果我将选择包含在另一个 on 上,结果是相同的(未排序):SELECT * FROM (SELECT ...) x ORDER BY DATE_VALID。我对其他结构相似的表也有同样的问题。
这是 Postgresql 9.2.8 的 EXPLAIN 结果:
Result (cost=0.02..62864.86 rows=10 width=87)
-> Merge Append (cost=0.02..62864.86 rows=10 width=87)
Sort Key: myTable.date_valid
-> Sort (cost=0.01..0.02 rows=1 width=220)
Sort Key: myTable.date_valid
-> Seq Scan on myTable (cost=0.00..0.00 rows=1 width=220)
Filter: ((date_valid >= '2014-07-03 09:00:00'::timestamp without time zone) AND (date_valid <= '2014-07-03 21:00:00'::timestamp without time zone) AND (id_variable = ANY ('{11012,12004}'::integer[])) AND ((id
_stn)::text = '78224'::text))
-> Index Scan using myTable_201407_ukey on myTable_201407 myTable (cost=0.00..62864.71 rows=9 width=72)
Index Cond: ((date_valid >= '2014-07-03 09:00:00'::timestamp without time zone) AND (date_valid <= '2014-07-03 21:00:00'::timestamp without time zone) AND (id_variable = ANY ('{11012,12004}'::integer[])))
Filter: ((id_stn)::text = '78224'::text)
最佳答案
可能这个错误在 9.2.1 中修复了
Fix possible incorrect sorting of output from queries involving WHERE indexed_column IN (list_of_values)
http://www.postgresql.org/docs/9.2/static/release-9-2-1.html
9.2 已经是 9.2.8
关于索引字段上的 Postgresql 9.2 时间戳排序不会在一天内按小时部分排序,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/24687898/