>Hi
>THe exection plan should show you the SQL statement, doesn't it?
>
>Anyway, can refer to http://social.msdn.microsoft.com/Forums/en-US/sqldataaccess/thread/7e5e08d0-2ef3-4858-b4cf-c73541edc178
>
>I have tried to change UNION => UNION ALL, the performance has improved from 4 mins to 1 min ++
>But still far from 2 secs (with UNION, but witout additional field from tableB)

Have you tried adding NOEXPAND hint? Also, what is the WHERE condition and which table fields in the WHERE belong to?