使用FULLTEXT的SQL Server 2012性能问题

Question

I'm using SQL Server 2012 Standard and I have some issue using the CONTAINS clause on a query.

My query:

select * 
from 
    calles as c 
INNER JOIN 
    colonias as col ON c.ID_Colonia = col.ID_Colonia
where 
    CONTAINS(c.Nombre,@Busqueda) OR CONTAINS(col.Nombre,@Busqueda)

If I use only one contains the time of the search is about 200 ms but if I use both it is about 10s (that's a lot of time). I try a workaround to do it using UNION like this:

select * 
from 
    calles as c 
INNER JOIN 
    colonias as col ON c.ID_Colonia = col.ID_Colonia
where 
    CONTAINS(c.Nombre,@Busqueda) 

UNION 

select * 
from 
    calles as c 
INNER JOIN 
    colonias as col ON c.ID_Colonia = col.ID_Colonia
where 
    CONTAINS(col.Nombre,@Busqueda)

And the query time is about 200ms again. But I think that the second code is clumsy. Do I have some error?

Answer 1

FULLTEXT index in SQL Server is a service which is (kinda) external to the RDBMS engine.

It accepts the search string and returns a list of key values from the table (which need then to be joined with the table itself to be sure they're still there).

So in fact you are joining two more tables in your query and apply an OR condition to the result of the join.

SQL Server's optimizer is not especially smart when it comes to constructs like this.

Replacing an OR condition with a UNION is a legitimate and commonly used optimization technique.