postgres 表的数据量非常大，按天分表（1千五百万行）。检索范围可能几十个表，检索很慢。
order表结构：
产品 代码 名字 分组 生产时间
product code(单独索引) name group timed(单独索引)
mybatis查询：
select product, code, name, group, timed
FROM
( SELECT product, code, name, group, timed FROM order_20221201 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_20221202 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_20221203 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_20221204 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_20221205 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_20221206 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_20221207 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_20221208 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_20221209 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_202212010 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed desc
UNION ALL SELECT product, code, name, group, timed FROM order_202212011 where code = 'AAAA' and timed > '2022-12-01 00:00:00' and timed < '2022-12-01 00:00:00' order by timed des
) AS PP
OFFSET 0
LIMIT 5
问题1： 如果code=AAA在第五个表order_20221205 中，而且满足条件条数也大于5条，
是否第六个表以后不再检索，如果数据库本身五优化所有表都查询一遍，
如何能让第六个表以后不查询呢？（最好通过sql解决，如果java解决改动非常大）
问题2： 10个表1亿5千万条，检索时间大概是20秒，如果优化提交加锁速度呢？满足5秒检索
通过explian 看，也是使用的索引检索
问题3：第一检索非常慢，第二次检索就能稍微快些（数据已加载到缓存中），换个检索区间又非常慢
使用场景，大部分时间是第一次检索，如何提高第一次检索速度？
问题4：windows 上postgres 如何清除缓存，不用每次重新启动电脑。
