IN的相關子查詢用EXISTS代替--sql2000性能優化

參考文章：SQL SERVER性能優化綜述(很好的總結,不要錯過哦)

數據庫：系統數據庫pubs

IN的相關子查詢用EXISTS代替，比如：

SELECT PUB_NAME FROM PUBLISHERS 
                WHERE PUB_ID IN (
                      SELECT PUB_ID 
                       FROM TITLES 
                        WHERE TYPE = 'BUSINESS') 

改進如下：

SELECT PUB_NAME  FROM PUBLISHERS 
WHERE EXISTS (
     SELECT 1 
     FROM TITLES 
     WHERE TYPE = 'BUSINESS' AND  PUB_ID= PUBLISHERS.PUB_ID)