SQL Server性能调优杂记（四）

这前后2种SQL文，在执行计划上有差异，所以导致一快一慢。后者竟然可以慢到17秒之多（第一产生执行计划的时候），即使马上再执行也有10秒到15秒，改善不大。

看一下SQL文1的执行计划

SQL文2的执行计划

前后最大的差别就是多了中间的Filter.

Filter这一步对于整个性能的影响很明显。而这步处理的工作就是原本我们SQL文意图中要忽略掉的部分。

所以，千万要小心，当用SQLCommand的动态参数为你的应用程序带来共通化方便的同时，也会让你程序带来性能问题的风险。

解决问题的方法，显然不能修改程序代码（换成动态自己产生SQL文），因为这是基础框架代码。

只能把SQL文改写一下

BEGIN
IF NOT(@CWB_NO IS NULL)
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　
ELSE
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.AWB_NO = @AWB_NO OR @AWB_NO IS NULL)
AND　(a.BWB_NO = @BWB_NO OR @BWB_NO IS NULL)
AND　(a.IE_TYPE = @IE_TYPE OR @IE_TYPE IS NULL)
AND　(a.CREATED_ON >= @DateFrom OR @DateFrom IS NULL)
AND (a.CREATED_ON <=　@DateTo OR @DateTo IS NULL)
AND (a.PAYMENT = @PAYMENT OR @PAYMENT IS NULL)
AND (a.ORIGIN = @ORIGIN OR @ORIGIN IS NULL)
AND (a.DEST = @DEST OR @DEST IS NULL)
AND (a.CONSIGNOR_CUSTOMER_CODE = @CONSIGNOR_CUSTOMER_CODE OR @CONSIGNOR_CUSTOMER_CODE IS NULL)
AND (a.CONSIGNOR_NAME LIKE ''%'' + @CONSIGNOR_NAME + ''%'' OR @CONSIGNOR_NAME IS NULL)
AND (a.CONSIGNEE_NAME LIKE ''%'' + @CONSIGNEE_NAME + ''%'' OR @CONSIGNEE_NAME IS NULL)
AND (a.CWB_TYPE = @CWB_TYPE OR @CWB_TYPE IS NULL)
END

结果SQL文的执行计划就正确了。