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sqlserver关于分页存储过程的优化【让数据库按我们的意思执行查询计划】 - 站长搜索
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sqlserver关于分页存储过程的优化【让数据库按我们的意思执行查询计划】

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2022-09-23 20:41:40 转载来源: 网络整理/侵权必删

复制代码代码如下:--代码一DECLARE@ccINTSELECTNewsId,ROW_NUMBER()OVER(ORDERBYSortNumDESC)ASRowIndexINTO#tbFROMnewsWITH(NOLOCK)WHERENewsTypeId=@NewsTypeIdANDIsShow=1SET@cc=@@ROWCOUNTSELECTn.*FROMnewsASnWITH(NOLOCK),#tbAstWHEREt.RowIndex>@PageIndex*@PageSizeANDt.RowIndex<=(@PageIndex+1)*@PageSizeANDt.newsid=n.newsidSELECT@ccDROPTABLE#tb复制代码代码如下:--代码二DECLARE@ccINTSELECTNewsId,ROW_NUMBER()OVER(ORDERBYSortNumDESC)ASRowIndexINTO#tbFROMnewsWITH(NOLOCK)WHERENewsTypeId=@NewsTypeIdANDIsShow=1SET@cc=@@ROWCOUNTSEL

复制代码 代码如下:

--代码一DECLARE @cc INT
SELECT NewsId,ROW_NUMBER() OVER(ORDER BY SortNum DESC) AS RowIndex INTO #tb FROM news WITH(NOLOCK) WHERE NewsTypeId=@NewsTypeId AND IsShow=1
SET @cc = @@ROWCOUNT
SELECT n.* FROM news AS n WITH(NOLOCK), #tb As t WHERE t.RowIndex>@PageIndex*@PageSize AND t.RowIndex<=(@PageIndex+1)*@PageSize AND t.newsid=n.newsid
SELECT @cc
DROP TABLE #tb

复制代码 代码如下:

--代码二
DECLARE @cc INT
SELECT NewsId,ROW_NUMBER() OVER(ORDER BY SortNum DESC) AS RowIndex INTO #tb FROM news WITH(NOLOCK) WHERE NewsTypeId=@NewsTypeId AND IsShow=1
SET @cc = @@ROWCOUNT
SELECT NewsId INTO #tb2 FROM #tb As t WHERE t.RowIndex>@PageIndex*@PageSize AND t.RowIndex<=(@PageIndex+1)*@PageSize
SELECT * FROM news WITH(NOLOCK) WHERE NewsId IN (SELECT * FROM #tb2)
SELECT @cc
DROP TABLE #tb
DROP TABLE #tb2

答案是代码二远远高于代码一。在代码一中加粗代码的操作会引起整表扫描,因为数据库引擎在认为WHERE表达式中满足条件记录大于一定阀值的时候,就不再去进行查询优化,而直接使用表扫描。看执行信息,:
表 'news'。扫描计数 1,逻辑读取 342 次,物理读取 0 次,预读 0 次,lob 逻辑读取 0 次,lob 物理读取 0 次,lob 预读 0 次。
(98361 行受影响)
(1 行受影响)
(40 行受影响)
表 '#tb________________________________________00000004C024'。扫描计数 1,逻辑读取 257 次,物理读取 0 次,预读 0 次,lob 逻辑读取 0 次,lob 物理读取 0 次,lob 预读 0 次。
表 'news'。扫描计数 1,逻辑读取 2805 次,物理读取 0 次,预读 235 次,lob 逻辑读取 0 次,lob 物理读取 0 次,lob 预读 0 次。
(1 行受影响)
(1 行受影响)

原本,我想的执行计划,加粗部分的代码应该是聚焦索引查找,这样性能就提高很多。看代码二:
表 'news'。扫描计数 1,逻辑读取 342 次,物理读取 0 次,预读 0 次,lob 逻辑读取 0 次,lob 物理读取 0 次,lob 预读 0 次。
(98361 行受影响)
(1 行受影响)
表 '#tb____________________________________00000004BEEF'。扫描计数 1,逻辑读取 257 次,物理读取 0 次,预读 0 次,lob 逻辑读取 0 次,lob 物理读取 0 次,lob 预读 0 次。
(40 行受影响)
(1 行受影响)
(40 行受影响)
表 'news'。扫描计数 0,逻辑读取 131 次,物理读取 0 次,预读 0 次,lob 逻辑读取 0 次,lob 物理读取 0 次,lob 预读 0 次。
表 '#tb2___________________________________00000004BEF0'。扫描计数 1,逻辑读取 2 次,物理读取 0 次,预读 0 次,lob 逻辑读取 0 次,lob 物理读取 0 次,lob 预读 0 次。
(1 行受影响)
(1 行受影响)

很明显,代码二与代码一中的IO操作数大大降低。且代码一随着@PageIndex越来越大,效率会越来越低;但代码二的效率不会随@PageIndex变化而改变。

标签: sqlserver 关于 分页 存储 过程 优化 数据库 我们 意思


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