当OR时，为什么SQL FullText查询会变慢？

Question

在SQL Server（2008）中，我在两列上有一个FullText索引，称之为Table1.FirstNames和Table2.LastNames。在分析了一些查询后，我想出了以下结果：

SELECT *
FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey)
WHERE CONTAINS(FirstNames, 'Bob') OR CONTAINS(LastNames, 'Bob')

=＆GT; 31 197ms

SELECT *
FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey)
WHERE (FirstNames LIKE '%Bob%') OR CONTAINS(LastNames, 'Bob')

=＆GT; 1941ms

SELECT *
FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey)
WHERE CONTAINS(FirstNames, 'Bob') OR LastNames LIKE '%Bob%'

=＆GT; 3201ms

SELECT *
FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey)
WHERE CONTAINS(FirstNames, 'Bob')

=＆GT; 565ms

SELECT *
FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey)
WHERE FirstNames LIKE '%Bob%'

=＆GT; 670ms

SELECT *
FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey)
WHERE CONTAINS(LastNames, 'Bob')

=＆GT; 17MS

SELECT *
FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey)
WHERE LastNames LIKE '%Bob%'

=＆GT; 3ms的

即使重建FullText索引，此行为仍然存在。

对于特定语言的大型数据集，FullText通常比LIKE查询快得多，但为什么当我将两个FullText碰撞时，查询速度减慢一个数量级？

Answer 1

更改为使用ContainsTable有帮助吗？

它在这里Adding more OR searches with CONTAINS Brings Query to Crawl

同一个回答者（Joe Stefanelli）通过将FREETEXT个谓词与OR一起更改为FREETEXTTABLE SQL Server full text query across multiple tables - why so slow? <，设法带来了类似的改进/ p>

Answer 2

也许您应该阅读：SQL Server 2005 Full-Text Queries on Large Catalogs: Lessons Learned。

Answer 3

我会看看每个人的执行计划。我猜你会从中学到很多东西。

Here is a decent link将向您展示如何显示执行计划以及解释它的一些提示。