Question

我有一个SQLite Database，我在其中使用以下query从两个表中获取数据。

select ie.* 
from (select * 
      from History where Station = @station and TimeStampCome <= @till and TimeStampCome >= @from 
      union all 
      select * 
      from Pending where Station = @station and TimeStampCome <= @till and TimeStampCome >= @from
     ) ie 
order by TimeStampCome desc LIMIT 100 OFFSET 1

这是最好和最有效的方式吗？我已将alarm objects存储在database中。因此，可以轻松地输入超过1百万个条目。

Answer 1

对于您的特定查询，最好先限制每个表中的行，如下所示：

with h as (
      select h.*
      from history h
      where Station = @station and TimeStampCome <= @till and TimeStampCome >= @from 
      order by TimeStampCome desc
      limit 101
     ),
     p as (
      select p.*
      from pending p
      where Station = @station and TimeStampCome <= @till and TimeStampCome >= @from 
      order by TimeStampCome desc
      limit 101
     )
select pe.*
from (select h.* from h union all
      select p.* from p
     ) pe
order by TimeStampCome desc
limit 100 offset 1;

但是，如果您开始使用不同的偏移量，这就变得不太可行了。

请注意，如果需要考虑性能，请从两个表中(Station, TimeStampCome)的索引开始。

SQLite |从两个（模式）相同的表中检索数据

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