數據庫環境：SQL SERVER 2005

今天在生產庫里抓到一條跑得慢的SQL，語句不是很復雜，返回的數據才有800多行，

卻執行了34分鐘，甚至更久。

先看一下執行結果

我貼一下SQL。

SELECT  a.dec_yt1 ,        b.dec_yt1 ,        a.dec_yt2 ,        b.dec_yt2 ,        a.dec_yt3 ,        b.dec_yt3FROM    ctlm8288 a ,        ( SELECT    t.corr_id ,                    t.clerk_id ,                    ROUND(SUM(ISNULL(t.dec_yt1, 0)), 2) AS dec_yt1 ,                    ROUND(SUM(ISNULL(t.dec_yt2, 0)), 2) AS dec_yt2 ,                    ROUND(SUM(ISNULL(t.dec_yt3, 0)), 2) AS dec_yt3          FROM      ( SELECT    b.corr_id ,                                b.clerk_id ,                                CASE WHEN d.feetype_flag = '1'                                     THEN ROUND(SUM(a.dec_sqty * c.fee_PRice),                                                2)                                END AS dec_yt1 ,                                CASE WHEN d.feetype_flag = '2'                                     THEN ROUND(SUM(a.dec_sqty * c.fee_price),                                                2)                                END AS dec_yt2 ,                                CASE WHEN d.feetype_flag = '3'                                     THEN ROUND(SUM(a.dec_sqty * c.fee_price),                                                2)                                END AS dec_yt3                      FROM      ctlm8666 a ,                                ctlm8001 b ,                                v_saft04 c ,                                ctlm8206 d                      WHERE     a.terminal_id = b.terminal_id                                AND b.dept_id = c.dept_id                                AND a.item_id = c.vitem_id                                AND c.fee_id = d.fee_id                                AND d.flag_t = 'Y'                                AND a.fiscal_year = 2015                                AND a.fiscal_period <= 6                                AND c.cur_year = 2015                                AND b.tertype_id LIKE '0102%'                      GROUP BY  b.corr_id ,                                b.clerk_id ,                                c.fee_id ,                                d.feetype_flag                    ) t          GROUP BY  t.corr_id ,                    t.clerk_id        ) bWHERE   a.corr_id = b.corr_id        AND a.clerk_id = b.clerk_id        AND a.fiscal_year = 2015        AND a.fiscal_period = 6

SQL的寫法沒太大問題，我試著執行下，然后就是漫長的等待過程...

30分過去了，還沒出結果，我看了執行計劃，就知道問題出在哪了。