联合与或

发布于 2024-09-07 02:52:22 字数 536 浏览 3 评论 0原文

假设我有两个查询：

select top 20 idField, field1, field2 from table1
where idField in
    (
    select idField from table1 where field3 like '...'
    union
    select idField from table2 where field4 like '...'
    )
order by sortfield1

select top 20 idField, field1, field2 from table1
where field3 like '...' 
or idfield in 
(select idField from table2 where field4 like '...')
order by sortfield1

假设两个表都相当大（表 2 大于表 1），结果数的平均范围是 0-400，但我总是想要最多 20 个结果。

是否有可能以很大的概率说出哪种语句性能更高和/或声明的选择取决于什么？谢谢

原文

let's say I've got two queries:

select top 20 idField, field1, field2 from table1
where idField in
    (
    select idField from table1 where field3 like '...'
    union
    select idField from table2 where field4 like '...'
    )
order by sortfield1

select top 20 idField, field1, field2 from table1
where field3 like '...' 
or idfield in 
(select idField from table2 where field4 like '...')
order by sortfield1

let's say that both tables are rather large (table2 larger than table1),
average range of results number is 0-400, but I always want max 20 results.

Is it possible to say with big probability which statement would be more performant
and/or what would the choice of statement depend on?
Thank you

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

路弥 2024-09-14 02:52:22

在完美的世界中，这应该不会产生影响，但我仍然会尝试这种方法。可以更快：

select top 20 idField, field1, field2 from table1
where idField in
    (
    select top 20 idField from table1 where field3 like '...'
    union
    select top 20 idField from table2 where field4 like '...'
    )

In the perfect world this should not make a difference, but I would still try out this approach too. Could be faster:

select top 20 idField, field1, field2 from table1
where idField in
    (
    select top 20 idField from table1 where field3 like '...'
    union
    select top 20 idField from table2 where field4 like '...'
    )

回复收藏 0 原文