這個例子和上面一個例子結果相反。
SQL文1
declare @CWB_NO varchar(50)
set @cwb_no='31301379874'
SELECT a.AWB_NO,
a.BWB_NO,
a.CWB_NO,
a.ORIGIN,
a.DEST,
a.MODIFY_ON,
a.CREATED_ON,
a.CONSIGNOR_CUSTOMER_CODE,
a.CONSIGNOR_CODE,
a.CONSIGNOR_NAME,
a.CONSIGNEE_NAME,
a.CWB_STATUS,
a.CWB_TYPE,
ISNULL(a.PCS, 0) AS PCS,
a.BWBLIST,
b.PWEIGHT
FROM TB_CWB AS a
LEFT JOIN TB_CWBWEIGHT AS b
ON a.CWB_NO = b.CWB_NO
AND b.AVAILABLE = 'Y'
WHERE a.AVAILABLE = 'Y'
AND (a.CWB_NO = @CWB_NO OR
(( @CWB_NO IS NULL)
AND (a.AWB_NO = NULL OR NULL IS NULL)
AND (a.BWB_NO = NULL OR NULL IS NULL)
AND (a.IE_TYPE = NULL OR NULL IS NULL)
AND (a.CREATED_ON >= NULL OR NULL IS NULL)
AND (a.CREATED_ON <= NULL OR NULL IS NULL)
AND (a.PAYMENT = NULL OR NULL IS NULL)
AND (a.ORIGIN = NULL OR NULL IS NULL)
AND (a.DEST = NULL OR NULL IS NULL)
AND (a.CONSIGNOR_CUSTOMER_CODE = NULL OR NULL IS NULL)
AND (a.CONSIGNOR_NAME LIKE '%' + NULL + '%' OR NULL IS NULL)
AND (a.CONSIGNEE_NAME LIKE '%' + NULL + '%' OR NULL IS NULL)
AND (a.CWB_TYPE = NULL OR NULL IS NULL)))
SQL Server根據這句SQL文執行產生的計劃
在這個計劃中，SQL Server更多考慮是2個大數據量表的情況，採納了分別按聚集索引獲取數據並採用並行處理過濾掉數據後，在進行連接，在並行處理的執行計劃。
在只查找一條記錄的時候，缺不是最佳的。沒有采用2個表的外鍵，我認爲是預編譯的SQL文，SQLServer是從查詢結果是大數據量的角度來選擇執行計劃。結果這句語句需要花費7秒到16秒。
換一種寫法，SQL 2
SELECT a.AWB_NO,
a.BWB_NO,
a.CWB_NO,
a.ORIGIN,
a.DEST,
a.MODIFY_ON,
a.CREATED_ON,
a.CONSIGNOR_CUSTOMER_CODE,
a.CONSIGNOR_CODE,
a.CONSIGNOR_NAME,
a.CONSIGNEE_NAME,
a.CWB_STATUS,
a.CWB_TYPE,
ISNULL(a.PCS, 0) AS PCS,
a.BWBLIST,
b.PWEIGHT
FROM TB_CWB AS a
LEFT JOIN TB_CWBWEIGHT AS b
ON a.CWB_NO = b.CWB_NO
AND b.AVAILABLE = 'Y'
WHERE a.AVAILABLE = 'Y'
AND (a.CWB_NO = '31301379874' OR
(( '31301379874' IS NULL)
AND (a.AWB_NO = NULL OR NULL IS NULL)
AND (a.BWB_NO = NULL OR NULL IS NULL)
AND (a.IE_TYPE = NULL OR NULL IS NULL)
AND (a.CREATED_ON >= NULL OR NULL IS NULL)
AND (a.CREATED_ON <= NULL OR NULL IS NULL)
AND (a.PAYMENT = NULL OR NULL IS NULL)
AND (a.ORIGIN = NULL OR NULL IS NULL)
AND (a.DEST = NULL OR NULL IS NULL)
AND (a.CONSIGNOR_CUSTOMER_CODE = NULL OR NULL IS NULL)
AND (a.CONSIGNOR_NAME LIKE '%' + NULL + '%' OR NULL IS NULL)
AND (a.CONSIGNEE_NAME LIKE '%' + NULL + '%' OR NULL IS NULL)
AND (a.CWB_TYPE = NULL OR NULL IS NULL)))
這句SQL文的執行計劃如下
SQL Server採用了比較好的執行計劃。因爲涉及記錄只有一條。先通過外鍵找到TB_CWBWeight的記錄，然後過濾，再和聚集索引找到的TB_CWB表記錄做數據合併。實際執行時間1秒都不到。
2者相差很大。
感覺，如果是單條查找，SQL文2的寫法應該比較好，SQL Server選擇執行計劃不會失誤。而採用存儲過程寫法的時候，還是要考慮有可能失誤的情況。所以，一般存儲過程中不應該寫冗長的SQL文，而是竟可能拆解成更簡單的SQL文，至少你可以用臨時表來獲得優化。