SQL Server - 比较NULL非常慢

Question

我想加快以下查询

WHERE子句中有两个条件(参见下面的查询以供参考)

目前,大约需要60秒.但是,如果我删除where子句中的第一个条件(@Query为NULL),则它几乎立即返回.

有关如何加快速度的想法吗？表中约有700k行,这只会增长.

(注意:下面显示的查询被剥离为它的本质,我严格使用硬编码值来简化查询,以便将焦点引向上面概述的部分)

declare @Query nvarchar(255)
select @Query = 'oceans'

select
    * 
from

(select 
  row_number() over( order by b.BookTitle) as RowNumber, 
  b.*
from
  Books b (nolock)
where
 -- If I remove this first condition "@Query is NULL", then it returns almost immediately
 -- Otherwise if I keep this here, it takes around 1 minute
 -- Yes, I have full-text index on BookTitle, as well as a regular index.
  (@Query is NULL) or (contains(b.BookTitle, @Query))
) as t1

where t1.RowNumber between 40 and 60

Answer 1

你能把它分成两个查询吗？ or通常会导致优化器出现问题:

if @Query is null
begin
    select * 
    from (select row_number() over( order by b.BookTitle) as RowNumber, b.*
          from Books b (nolock)
          where @Query is NULL
         ) as t1
    where t1.RowNumber between 40 and 60;
end
else
begin
    select * 
    from (select row_number() over( order by b.BookTitle) as RowNumber, b.*
          from Books b (nolock)
          where contains(b.BookTitle, @Query)
         ) as t1
    where t1.RowNumber between 40 and 60;
end