>Probably I don't understand the type of query you are doing. If you have all the values hardcoded then go with that.

Here is an example:

SELECT Thread.Numero
 FROM Thread
 WHERE Thread.NoStatus=1 AND (Thread.NoClient=1 OR Thread.NoClient=2)

That specific one can benefit of a compound index on NoStatus+NoClient.

SELECT Thread.Numero
 FROM Thread
 WHERE Thread.NoStatus=1 AND
  EXISTS (SELECT ForumCli.Numero FROM ForumCli WHERE ForumCli.NoMember=1 AND (ForumCli.NoClient=1 OR ForumCli.NoClient=2))

That specific one uses the EXISTS to see if the child table has records.