SQL Server - 与 NULL 相比非常慢

Question

我想加快下面的查询

WHERE子句中有两个条件(引用下面的查询)

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)，它几乎会立即返回。

关于如何加快速度的任何想法？表中大约有 70 万行，而且只会增长。

(注意:下面显示的查询被剥离到它的本质，我严格使用硬编码值来简化查询，以便将焦点吸引到上面概述的部分)

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 通常会给优化器带来问题:

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